SiC epitaxial wafer, manufacturing apparatus of SiC epitaxial wafer, fabrication method of SiC epitaxial wafer, and semiconductor device

ABSTRACT

A SiC epitaxial wafer includes: a substrate having an off angle of less than 4 degrees; and a SiC epitaxial growth layer disposed on the substrate having the off angle of less than 4 degrees, wherein an Si compound is used for a supply source of Si, and a C compound is used as a supply source of C, for the SiC epitaxial growth layer, wherein the uniformity of carrier density is less than 10%, and the defect density is less than 1 count/cm 2 ; and a C/Si ratio of the Si compound and the C (carbon) compound is within a range of 0.7 to 0.95. There is provide a high-quality SiC epitaxial wafer excellent in film thickness uniformity and uniformity of carrier density, having the small number of surface defects, and capable of reducing costs, also in low-off angle SiC substrates on SiC epitaxial growth.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application (CA) of PCT Application No.PCT/JP2016/074794, filed on Aug. 25, 2016, which claims priority toJapan Patent Application No. P2015-182974 filed on Sep. 16, 2015 and isbased upon and claims the benefit of priority from prior Japanese PatentApplications No. P2015-182974 filed on Sep. 16, 2015 and PCT ApplicationNo. PCT/JP2016/074794, filed on Aug. 25, 2016, the entire contents ofeach of which are incorporated herein by reference.

FIELD

The embodiments described herein relate a SiC epitaxial wafer, amanufacturing apparatus of the SiC epitaxial wafer, a fabrication methodof the SiC epitaxial wafer, and a semiconductor device.

BACKGROUND

In recent years, much attention has been given to Silicon Carbide (SiC)semiconductors capable of realizing high breakdown voltage, high currentuse, low on resistance, high degree of efficiency, power consumptionreduction, high speed switching, etc., since the SiC semiconductors havewider bandgap energy and higher breakdown voltage performance at highelectric field, compared with Silicon (Si) semiconductors or GalliumArsenide (GaAs) semiconductors. The SiC has received attention also interms of environmental protections since occurrence of carbon dioxidegas (CO₂) can be reduced due to the low power consumption performancethereof.

Recently, the SiC devices have been applied to many applicable fields,e.g. air-conditioning apparatuses (air-conditioners), solar powergeneration systems, automobile systems, and train-vehicle systems.

Since SiC compound semiconductors capable of taking equal to or greaterthan 200 types of crystal polymorphisms, there may be stable structuresdifferent between a substrate (bulk) and an epitaxial growth layerformed on the substrate. Accordingly, the epitaxial growth layer formedon the SiC substrate having an off angle is 0 degree may include manycrystal defects. Accordingly, it is general to provide an off angle inthe substrate in order to form the SiC epitaxial growth layer.

In such a situation, one of the important problems in a case of applyingthe SiC is a point of cost. As a detail of the costs of SiC devices,wafer costs account for approximately 50%, SiC epitaxial growth costsaccount for approximately 22%, and fabrication process costs account forapproximately 28%. For example, it is advantageous to use 150-mm(6-inch) φ wafers in terms of reducing the SiC device fabrication costsper unit area. However, it is general to use substrates having an offangle of 4 degrees, as the present 6-inch φ SiC wafers.

One method for a cost reduction of the SiC devices is to reduce such anoff angle of the SiC substrate. However, if low-off angle substrates areused, it is difficult to realize high-quality epitaxial growth.

There has also already been reported results of SiC epitaxial growthperformed on 4H—SiC substrates having an off angle of 2 degrees, fromsome groups. According to these reports, doping uniformity and filmthickness uniformity can be satisfactorily controlled. However,occurrence of step bunching is increased and a triangular defect densityis also increased, compared with SiC epitaxial growth on the SiCsubstrates having the off angle of 4 degrees. On the other hand,occurrence of the triangular defect can be relatively suppressed underhigh growth temperatures.

SUMMARY

Also for such low-off angle SiC substrates on the SiC epitaxial growthlayers, it is desired to provide a SiC epitaxial growth technique whichis capable of reducing occurrence of such step bunching or a triangulardefect density, and is excellent in film thickness uniformity anduniformity of carrier density in a tradeoff relationship with thereduction of the defect density, and is capable of reducing the costs.

The embodiments provide: a high-quality SiC epitaxial wafer excellent infilm thickness uniformity and uniformity of carrier density, having thesmall number of surface defects, and capable of reducing costs, also inlow-off angle SiC substrates on SiC epitaxial growth; a manufacturingapparatus of such a SiC epitaxial wafer; a fabrication method of such aSiC epitaxial wafer; and a semiconductor device.

According to one aspect of the embodiments, there is provided a SiCepitaxial wafer comprising: a substrate having low-off angle of lessthan 4 degrees; and a SiC epitaxial growth layer disposed on thesubstrate, wherein an Si compound is used for a supply source of Si, anda Carbon (C) compound is used as a supply source of Carbon (C), for theSiC epitaxial growth layer, wherein the uniformity of carrier density isless than 10%, and the defect density is less than 1 count/cm²; and aC/Si ratio between the Si compound and the Carbon (C) compound is withina range of 0.7 to 0.95.

According to another aspect of the embodiments, there is provided afabrication method of a SiC epitaxial wafer comprising: preparing a SiCingot, cutting the prepared SiC ingot with an off angle of less than 4degrees, and polishing the cut SiC ingot to form a SiC bare wafer;removing a cut surface of the SiC bare wafer to form a SiC substratehaving the off angle of less than 4 degrees; and crystal-growing a SiCepitaxial growth layer on the SiC substrate, wherein a material gas tobe supplied contains an Si compound used as a supply source of Si, andCarbon (C) compound used as a supply source of Carbon (C), wherein theuniformity of carrier density is less than 10%, and the defect densityis less than 1 count/cm²; and a C/Si ratio between the Si compound andthe Carbon (C) compound is within a range of 0.7 to 0.95.

According to still another aspect of the embodiments, there is provideda manufacturing apparatus of a SiC epitaxial wafer comprising: a gasinjection port; a gas exhaust port; a heating unit; and a reactor,wherein a material gas supplied when forming the SiC epitaxial growthlayer on the substrate having the off angle of less than 4 degreescontains an Si compound used as a supply source of Si, and Carbon (C)compound used as a supply source of Carbon (C), wherein the uniformityof carrier density is less than 10%, and the defect density is less than1 count/cm²; and a C/Si ratio between the Si compound and the Carbon (C)compound is within a range of 0.7 to 0.95.

According to yet another aspect of the embodiments, there is provided asemiconductor device comprising the above-mentioned SiC epitaxial wafer.

According to the embodiments, there can be provided: the high-qualitySiC epitaxial wafer excellent in film thickness uniformity anduniformity of carrier density, having the small number of surfacedefects, and capable of reducing costs, also in low-off angle SiCsubstrates on SiC epitaxial growth; the manufacturing apparatus of sucha SiC epitaxial wafer; the fabrication method of such a SiC epitaxialwafer; and the semiconductor device.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic bird's-eye view configuration diagram of a SiCepitaxial wafer according to the embodiments.

FIG. 1B is a schematic bird's-eye view configuration diagram of the SiCepitaxial wafer according to the embodiments, in which a SiC epitaxialgrowth layer includes a double layer structure having a buffer layer anda drift layer.

FIG. 2A is a schematic bird's-eye view configuration diagram showing aunit cell of a 4H—SiC crystal applicable to the SiC epitaxial waferaccording to the embodiments.

FIG. 2B is a schematic configuration diagram showing a two-layer portionof the 4H—SiC crystal.

FIG. 2C is a schematic configuration diagram showing the unit cell ofthe 4H—SiC crystal.

FIG. 3 is a schematic configuration diagram showing the unit cell of the4H—SiC crystal shown in FIG. 2A observed from directly above a (0001)surface.

FIG. 4A is a process chart of: preparing a hexagonal-crystal SiC ingot;cutting the SiC ingot with an off angle θ of less than 4 degrees withrespect to the (0001) surface; and then polishing the cut SiC ingot toform a plurality pieces of SiC bare wafers, in a schematic bird's-eyeview structure diagram showing a fabrication method of the SiC epitaxialwafer according to the embodiments.

FIG. 4B is a process chart of removing a cut surface ((0001) surface) ofthe SiC bare wafer by equal to or greater than 500 nm, after a machiningprocess.

FIG. 4C is a process chart of forming an oxide film on a main face ofthe SiC substrate by applying an oxidation treatment to the main face((0001) surface) of the SiC substrate.

FIG. 4D is a process chart of forming a SiC epitaxial growth layer on aSiC substrate having an off angle of less than 4 degrees.

FIG. 5 shows an example of a photograph of a hexagonal-crystal SiC ingotfrom which the SiC epitaxial wafer is cut.

FIG. 6A is a schematic explanatory diagram showing an example of cuttingthe SiC epitaxial wafer from the SiC ingot at the off angle of 4degrees, as a comparative example.

FIG. 6B is a schematic explanatory diagram showing an example of cuttingthe SiC epitaxial wafer from the SiC ingot at the off angle of twodegrees.

FIG. 7 is a relational chart between yield Y (%) and a device sidelength (mm), using a defect density (count(s)/cm²) as a parameter.

FIG. 8A is an explanatory diagram of an aspect of a conversion from aBasal Plane Dislocation (BPD) to a Threading Edge Dislocation (TED), ina case where an off angle is relatively large when forming the SiCepitaxial growth layer on the SiC substrate.

FIG. 8B is an explanatory diagram showing an aspect of the conversionfrom BPD to TED when the off angle is relatively small.

FIG. 9A is a schematic cross-sectional structure diagram in a gas flowchannel direction showing an epitaxial growth apparatus applied whenforming the SiC epitaxial growth layer on the SiC substrate having anoff angle of 2 degrees according to the embodiments.

FIG. 9B is a schematic cross-sectional structure diagram in a directionvertical to the gas flow channel showing the epitaxial growth apparatusapplied when forming the SiC epitaxial growth layer on the SiC substratehaving the off angle of 2 degrees according to the embodiments.

FIG. 10 is a schematic plain diagram showing a configuration ofarranging two 3-inch wafers in parallel in a 6-inch wafer pocket on aholder plate at the time of epitaxial growth, in the epitaxial growthapparatus applied when forming the SiC epitaxial growth layer on the SiCsubstrate having the off angle of 2 degrees according to theembodiments.

FIG. 11 is a diagram of comparing a surface morphology limit between theoff angle of 4 degrees and the off angle of 2 degrees, in a relationshipbetween a growth temperature T_(g) and a C/Si ratio of material gasshowing satisfactory surface flatness when forming the SiC epitaxialgrowth layer on the SiC substrate.

FIG. 12A shows an image of confocal differential interference microscope(field of view: 750×750 μm²) of the SiC epitaxial growth layer formed onthe SiC substrate having the off angle of 2 degrees shown in FIG. 11, ina case where the growth temperature T_(g) is 1680° C., the C/Si ratio is0.8, and a HAZE value is 5.7.

FIG. 12B shows an image of confocal differential interference microscope(field of view: 750×750 μm²) of the SiC epitaxial growth layer formed onthe SiC substrate having the off angle of 2 degrees shown in FIG. 11, ina case where the growth temperature T_(g) is 1680° C., the C/Si ratio is0.9, and a HAZE value is 5.9.

FIG. 12C shows an image of confocal differential interference microscope(field of view: 750×750 μm²) of the SiC epitaxial growth layer formed onthe SiC substrate having the off angle of 2 degrees shown in FIG. 11, ina case where the growth temperature T_(g) is 1650° C., the C/Si ratio is0.7, and a HAZE value is 5.5.

FIG. 12D shows an image of confocal differential interference microscope(field of view: 750×750 μm²) of the SiC epitaxial growth layer formed onthe SiC substrate having the off angle of 2 degrees shown in FIG. 11, ina case where the growth temperature T_(g) is 1650° C., the C/Si ratio is0.8, and a HAZE value is 5.5.

FIG. 12E shows an image of confocal differential interference microscope(field of view: 750×750 μm²) of the SiC epitaxial growth layer formed onthe SiC substrate having the off angle of 2 degrees shown in FIG. 11, ina case where the growth temperature T_(g) is 1650° C., the C/Si ratio is0.9, and a HAZE value is 5.7.

FIG. 13A shows an image of confocal differential interference microscope(field of view: 750×750 μm²) of the SiC epitaxial growth layer formed onthe SiC substrate having the off angle of 2 degrees shown in FIG. 11, ina case where the growth temperature T_(g) is 1710° C., the C/Si ratio is0.8, and a HAZE value is 19.7.

FIG. 13B shows an image of confocal differential interference microscope(field of view: 750×750 μm²) of the SiC epitaxial growth layer formed onthe SiC substrate having the off angle of 2 degrees shown in FIG. 11, ina case where the growth temperature T_(g) is 1710° C., the C/Si ratio is1.0, and a HAZE value is 27.7.

FIG. 13C shows an image of confocal differential interference microscope(field of view: 750×750 μm²) of the SiC epitaxial growth layer formed onthe SiC substrate having the off angle of 2 degrees shown in FIG. 11, ina case where the growth temperature T_(g) is 1680° C., the C/Si ratio is1.0, and a HAZE value is. 14.1.

FIG. 13D shows an image of confocal differential interference microscope(field of view: 750×750 μm²) of the SiC epitaxial growth layer formed onthe SiC substrate having the off angle of 2 degrees shown in FIG. 11, ina case where the growth temperature T_(g) is 1650° C., the C/Si ratio is1.0, and a HAZE value is 15.1.

FIG. 14 shows dependency of growth pressure P (kPa) of the defectdensity (cm⁻²) and uniformity (%) of carrier density (N_(D)-N_(A)) (thegrowth temperature T_(g) is 1680° C., a flow rate of carrier gas is 120slm-H₂, and a C/Si ratio is 0.9), in a result of forming the SiCepitaxial growth layer on the SiC substrate having the off angle of 2degrees according to the embodiments.

FIG. 15 shows dependency of flow rate of carrier gas (H² gas flow) (slm)of the defect density (cm⁻²) and the uniformity (%) of carrier density(N_(D)-N_(A)) (the growth temperature T_(g) is 1680° C. and the C/Siratio is 0.9, and the growth pressure P is 10.3 (kPa)), in a result offorming the SiC epitaxial growth layer on the SiC substrate having theoff angle of 2 degrees according to the embodiments.

FIG. 16 is an explanatory diagram showing a process window in arelationship between the growth temperature T_(g) (° C.) and the C/Siratio under the growth pressure P=10.3 (kPa), in a result of forming theSiC epitaxial growth layer on the SiC substrate having the off angle of2 degrees according to the embodiments.

FIG. 17 shows dependency of C/Si ratio of the defect density (cm⁻²) andthe uniformity (%) of carrier density (N_(D)-N_(A)) (the growthtemperature T_(g) is 1680° C., the flow rate of carrier gas is 120slm-H₂, and the growth pressure P is 10.3 (kPa)), in a result of formingthe SiC epitaxial growth layer on the SiC substrate having the off angleof 2 degrees according to the embodiments.

FIG. 18A shows a defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis an example of a downfall.

FIG. 18B shows a defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis another example of the downfall.

FIG. 18C shows a defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis still another example of the downfall.

FIG. 18D shows a defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis yet another example of the downfall.

FIG. 18E shows a defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis further example of the downfall.

FIG. 18F shows a defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis still further example of the downfall.

FIG. 19A shows a defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis an example of a carrot defect.

FIG. 19B shows a defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis another example of a carrot defect.

FIG. 19C shows a defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis still another example of a carrot defect.

FIG. 19D shows a defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis yet another example of a carrot defect.

FIG. 20A shows a defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis an example of a triangular defect.

FIG. 20B shows a defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis another example of a triangular defect.

FIG. 20C shows a defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis still another example of a triangular defect.

FIG. 20D shows a defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis yet another example of a triangular defect.

FIG. 21A shows defects which occur when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis an example of a downfall and a triangular defect.

FIG. 21B shows defects which occur when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees, whichis another example of a downfall and a triangular defect.

FIG. 22A is a schematic plain diagram showing a triangular defectexample, in an explanatory diagram showing an occurrence mechanism ofthe triangular defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle of 2 degrees.

FIG. 22B is a schematic cross-sectional diagram showing the triangulardefect example, in an explanatory diagram showing an occurrencemechanism of the triangular defect which occurs when the SiC epitaxialgrowth layer is formed on the SiC substrate having the off angle of 2degrees.

FIG. 23 is an explanatory diagram of reduction measures of a triangulardefect occurring when the SiC epitaxial growth layer is formed on theoff angle SiC substrate.

FIG. 24 is a diagram showing a relationship between a probability ofoccurrence (%) of a triangular defect and a thickness of the epitaxialgrowth layer, in a result of forming the SiC epitaxial growth layer onthe SiC substrate having the off angle of 2 degrees according to theembodiments (the number N of triangular defects=61).

FIG. 25A shows a defect density map on a 3-inch wafer (inside) arrangedside by side in a 6-inch wafer pocket, in a result of forming the SiCepitaxial growth layer on the SiC substrate having the off angle of 2degrees according to the embodiments.

FIG. 25B shows a defect density map on a 3-inch wafer (outside) arrangedside by side in a 6-inch wafer pocket, in a result of forming the SiCepitaxial growth layer on the SiC substrate having the off angle of 2degrees according to the embodiments.

FIG. 25C shows a defect density map on the 3-inch wafer (inside)arranged side by side in the 6-inch wafer pocket, in a result of formingthe SiC epitaxial growth layer (drift layer) via a buffer layer on theSiC substrate having the off angle of 2 degrees according to theembodiments.

FIG. 25D shows a defect density map on the 3-inch wafer (outside)arranged side by side in the 6-inch wafer pocket, in a result of formingthe SiC epitaxial growth layer (drift layer) via a buffer layer on theSiC substrate having the off angle of 2 degrees according to theembodiments.

FIG. 26 shows a schematic structure example in which a SiC epitaxialgrowth layer is formed on the SiC substrate having the off angle of 2degrees according to the embodiments (the growth temperature T_(g) is1670° C., the C/Si ratio is 0.9, the growth pressure P is 6.3 (kPa), andthe thickness of the SiC epitaxial growth layer is 5 μm).

FIG. 27 shows dependency of etching depth of a defect density (cm⁻²) anda reflection loss (a. u.), in a result of forming the SiC epitaxialgrowth layer on the SiC substrate having the off angle of 2 degreesaccording to the embodiments.

FIG. 28A is a schematic structure example in a result of forming a SiCepitaxial growth layer (drift layer) via a buffer layer on the SiCsubstrate having the off angle of 2 degrees according to the embodiments(the growth temperature T_(g) is 1680° C., the growth pressure P is 10.3(kPa), and the C/Si ratio of the buffer layer is 0.75, the thickness ofthe buffer layer is X μm, the C/Si ratio of the epitaxial growth layeris 0.9, and the thickness of the epitaxial growth layer is 10 μm).

FIG. 28B shows dependency of the defect density (cm⁻²) of the SiCepitaxial growth layer (drift layer) and the thickness X (μm) of thebuffer layer (the C/Si ratio=0.75), in a result of forming the SiCepitaxial growth layer (drift layer) via the buffer layer on the SiCsubstrate having the off angle of 2 degrees according to theembodiments.

FIG. 29 shows a typical example of an image of confocal differentialinterference microscope (field of view: 750×750 μm²) of the SiCepitaxial growth layer (drift layer) formed via the buffer layer on theSiC substrate having the off angle of 2 degrees (the growth temperatureis 1680° C., the C/Si ratio of the buffer layer is 0.75, the thicknessof the buffer layer is 0.5 μm, the C/Si ratio of the drift layer is 0.9,and the thickness of the drift layer is 10 μm).

FIG. 30 is a schematic configuration diagram showing a first CVDapparatus applicable to the SiC epitaxial growth, in a manufacturingapparatus of the SiC epitaxial wafer according to the embodiments.

FIG. 31 is a schematic configuration diagram showing a second CVDapparatus applicable to the SiC epitaxial growth, in a manufacturingapparatus of the SiC epitaxial wafer according to the embodiments.

FIG. 32 is a schematic configuration diagram showing a third CVDapparatus applicable to the SiC epitaxial growth, in a manufacturingapparatus of the SiC epitaxial wafer according to the embodiments.

FIG. 33 is a schematic configuration diagram showing a fourth CVDapparatus applicable to the SiC epitaxial growth, in a manufacturingapparatus of the SiC epitaxial wafer according to the embodiments.

FIG. 34 is a schematic cross-sectional structure diagram showing aSchottky barrier diode fabricated with the SiC epitaxial wafer accordingto the embodiments.

FIG. 35 is a schematic cross-sectional structure diagram showing atrench-gate type MOSFET fabricated with the SiC epitaxial waferaccording to the embodiments.

FIG. 36 is a schematic cross-sectional structure diagram showing aplanar-gate type MOSFET fabricated with the SiC epitaxial waferaccording to the embodiments.

DESCRIPTION OF EMBODIMENTS

Next, the embodiments will be described with reference to drawings. Inthe description of the following drawings, the identical or similarreference numeral is attached to the identical or similar part. However,it should be noted that the drawings are schematic and therefore therelation between thickness and the plane size and the ratio of thethickness differs from an actual thing. Therefore, detailed thicknessand size should be determined in consideration of the followingexplanation.

Of course, the part from which the relation and ratio of a mutual sizediffer also in mutually drawings is included.

Moreover, the embodiments shown hereinafter exemplify the apparatus andmethod for materializing the technical idea; and the embodiments do notspecify the material, shape, structure, placement, etc. of eachcomponent part as the following. The embodiments may be changed withoutdeparting from the spirit or scope of claims.

Embodiments

As shown in FIG. 1A, a SiC epitaxial wafer 1 according to theembodiments includes: a substrate 2 having an off angle of less than 4;and a SiC epitaxial growth layer 3 disposed on the substrate 2. In theembodiments, an Si (silicon) compound is used for a supply source of Si(silicon), and a Carbon (C) compound is used as a supply source ofCarbon (C), for the SiC epitaxial growth layer 3. In this context,uniformity of carrier density may be less than 10% and a defect densityis less than 1 count/cm²; and a C/Si ratio between the Si compound andthe Carbon (C) compound may be within a range of 0.7 to 0.95.

Moreover, as shown in FIG. 1B, the SiC epitaxial wafer 1 according tothe embodiments may include: a substrate 2 having an off angle of lessthan 4; and a SiC epitaxial growth layer 3 disposed on the substrate 2,wherein the SiC epitaxial growth layer 3 may include a buffer layer 3Bdisposed on the substrate 2, and a drift layer 3D disposed on the bufferlayer 3B. The uniformity of carrier density is less than 10%, and thedefect density is less than 0.5 count/cm²; and the C/Si ratio betweenthe Si compound and the Carbon (C) compound in the buffer layer 3B iscontrolled to be lower than the C/Si ratio between the Si compound andthe Carbon (C) compound in the drift layer 3D.

Moreover, the off angle of less than 4 degrees may be an angle of 2degrees, for example.

Moreover, a diameter of the substrate having the off angle may be equalto or greater than 100 mm, for example.

Moreover, a growth temperature of the SiC epitaxial growth layer 3 maybe within a range of 1630° C. to 1690° C.

Moreover, a growth pressure of the SiC epitaxial growth layer 3 may bewithin a range of 3 kPa to 11 kPa.

Moreover, a flow rate of carrier gas at the time of formation of the SiCepitaxial growth layer 3 may be within a range of 100 slm to 150 slm. Inthis context, the units “slm” is standard liter/min, and is a unitexpressing a flow rate per minute under 1 atm at 0° C. by the liter.

The Si compound may contain any one material of SiH₄, SiH₃F, SiH₂F₂,SiHF₃, or SiFP₄, for example. Other compounds containing chlorine (Cl)may be used as the Si compound.

Moreover, the C compound may contain any one material of C₃H₈, C₂H₄,C₂H₂, CF₄, C₂F₆, C₃F₈, C₄F₆, C₄F₈, CsF₈, CHF₃, CH₂F₂, CH₃F, or C₂HF₅.Other compounds containing chlorine (Cl) may be used as the C compound.

Moreover, the SiC epitaxial growth layer 3 may contain any one materialof 4H—SiC, 6H—SiC, 2H—SiC, or 3C—SiC.

The substrate 2 having an off angle of less than 4 may contain 4H—SiC or6H—SiC. Any one BN, AlN, Al₂O₃, Ga₂O₃, diamond, carbon, or graphite maybe contained instead of the SiC.

In the SiC epitaxial growth for the SiC epitaxial wafer according to theembodiments, at least one of H₂, Ar, HCl, and the F₂ is applicable ascarrier gas.

As materials for dopant, nitrogen (N) or Trimethylaluminium (TMA:(CH₃)₃Al) is applicable.

(SiC Epitaxial Wafer)

A schematic bird's-eye view configuration of the SiC epitaxial waferaccording to the embodiments is illustrated as shown in FIG. 1A or 1B.

The SiC epitaxial wafer 1 contains 4H—SiC, for example; and includes aSiC substrate 2 having an off angle of less than 4 degrees, and a SiCepitaxial growth layer 3 laminated on the SiC substrate 2. A thicknesst1 of the SiC substrate 2 is approximately 200 μm to approximately 500μm, for example, and a thickness t2 of the SiC epitaxial growth layer 3is approximately 4 μm to approximately 100 μm, for example.

Moreover, as shown in FIG. 1B, the SiC epitaxial growth layer 3 mayinclude a double layer structure between the buffer layer 3B and thedrift layer 3D, wherein: the uniformity of carrier density may be lessthan 10%, and the defect density may be less than 0.5 count/cm²; and theC/Si ratio between the Si compound and the Carbon (C) compound in thebuffer layer 3B may be controlled to be lower than the C/Si ratiobetween the Si compound and the Carbon (C) compound in the drift layer3D.

(Crystal Structure)

FIG. 2A shows a schematic bird's-eye view configuration of a unit cellin a 4H—SiC crystal applicable to the SiC epitaxial wafer 1 according tothe embodiments, FIG. 2B shows a schematic configuration of a two layerportion of the 4H—SiC crystal, and FIG. 2C shows a schematicconfiguration of a unit cell of the 4H—SiC crystal.

Moreover, FIG. 3 shows a schematic configuration of the unit cell of the4H—SiC crystal structure of shown in FIG. 2A observed from directlyabove a (0001) surface.

As shown in FIGS. 2A to 2C, the crystal structure of the 4H—SiC can beapproximated with a hexagonal system, and four C atoms are bound withrespect to one Si atom. The four C atoms are positioned at four vertexesof a regular tetrahedron in which the Si atom is disposed at a centerthereof. In the four C atoms, one Si atom is positioned in [0001] axialdirection with respect to the C atom, and other three C atoms arepositioned at a [000-1] axis side with respect to the Si atom.

The [0001] axis and [000-1] axis are along the axial direction of thehexagonal prism, and a surface (top surface of the hexagonal prism)using the [0001] axis as a normal line is (0001) surface (Si surface).On the other hand, a surface (bottom surface of the hexagonal prism)using the [000-1] axis as a normal line is (000-1) surface (C surface).

Moreover, directions vertical to the [0001] axis, and passing along thevertexes not adjacent with one another in the hexagonal prism observedfrom directly above the (0001) surface are respectively a1 axis[2-1-10], a2 axis [−12-10], and a3 axis [−1-120].

As shown in FIG. 3, a direction passing through the vertex between thea1 axis and the a2 axis is [11-20] axis, a direction passing through thevertex between the a2 axis and the a3 axis is [−2110] axis, and adirection passing through the vertex between the a3 axis and the a1 axisis [1-210] axis.

The axes which are incline at an angle of 30 degrees with respect toeach axis of the both sides, and used as the normal line of each sidesurface of the hexagonal prism, between each of the axes of theabove-mentioned six axes passing through the respective vertexes of thehexagonal prism, are respectively [10-10] axis, in the clockwisedirection sequentially from between the a1 axis and the [11-20] axes,[1-100] axis, [0-110] axis, [−1010] axis, [−1100] axis, and [01-10]axis. Each surface (side surface of the hexagonal prism) using theseaxes as the normal line is a crystal surface right-angled to the (0001)surface and the (000-1) surface.

(Fabrication Method of SiC Epitaxial Wafer)

A fabrication method of the SiC epitaxial wafer according to theembodiments includes: preparing a SiC ingot 13, cutting the prepared SiCingot 13 with an off angle θ of less than 4 degrees, and polishing thecut SiC ingot to form a SiC bare wafer 14; removing a cut surface of theSiC bare wafer 14 to form a SiC substrate 2 having an off angle of lessthan 4 degrees; forming an oxide film 16 on a principal surface of theSiC substrate 2; removing the oxide film 16; and crystal-growing a SiCepitaxial growth layer on the SiC substrate 2 having the off angle ofless than 4 degrees. In the embodiments, a material gas to be suppliedcontains an Si compound used as a supply source of Si, and Carbon (C)compound used as a supply source of Carbon (C). In this context,uniformity of carrier density may be less than 10% and a defect densityis less than 1 count/cm²; and a C/Si ratio between the Si compound andthe Carbon (C) compound is within a range of 0.7 to 0.95.

Moreover, the crystal-growing the SiC epitaxial growth layer 3 mayinclude: crystal-growing a buffer layer 3B on the SiC substrate 2; andcrystal-growing a drift layer 3D on the buffer layer 3B. In thiscontext, uniformity of carrier density may be less than 10% and a defectdensity is less than 0.5 count/cm²; and a C/Si ratio of the buffer layer3B is controlled to be lower than a C/Si ratio of the drift layer 3D.

The off angle θ may be 2 degrees.

Moreover, a diameter of the substrate having the off angle may be equalto or greater than 100 mm, for example.

Moreover, a growth temperature of the SiC epitaxial growth layer 3 maybe within a range of 1630° C. to 1690° C.

Moreover, a growth pressure of the SiC epitaxial growth layer 3 may bewithin a range of 3 kPa to 11 kPa.

Moreover, a flow rate of carrier gas at the time of formation of the SiCepitaxial growth layer 3 may be within a range of 100 slm to 150 slm.

Moreover, the SiC epitaxial growth layer 3 may contain any one of4H—SiC, 6H—SiC, 2H—SiC, or 3C—SiC.

For example, the SiC bare wafer 14 was obtained by cutting the 4H—SiCingot with an off angle of 2 degrees in the [11-20] axis direction withrespect to the (0001) surface. A diameter of the SiC bare wafer 14 isapproximately 150 mm.

Subsequently, the surface where the SiC bare wafer 14 is cut out issubjected to the polishing process, and then a suitable surface for theepitaxial wafer was obtained. In the polishing process, including abevel process of the wafer edge, etc., the polished surface was finishedby utilizing a chemical effect since it is not sufficiently able toremove processing damage merely by mechanical processes.

Before the epitaxial growth, the polished surface is sufficiently washedin order to clean the surface. In the embodiments, RCA washing, brushwashing, functional-water washing, megasonic washing, etc. can be used,as a washing method.

A pressure in a reactor after disposing the wafer is kept atapproximately 3 kPa to approximately 11 kPa, for example. H₂ used as acarrier gas of the materials is supplied into the reactor. An Ar gas maybe supplied thereinto instead of H₂. By mixing HCl or HF to the carriergas, a vapor phase reaction can be reduced, generation of particles onthe epitaxial wafer can be suppressed, and thereby a high quality wafercan be supplied.

FIG. 4A shows the processing step of preparing a hexagonal-crystal SiCingot 13, and cutting the SiC ingot 13 with an off angle θ of less than4 degrees with respect to the (0001) surface, and polishing the cut SiCingot 13 to form a plurality pieces of SiC bare wafers 14, in aschematic bird's-eye view configuration showing the fabrication methodof the SiC epitaxial wafer according to the embodiments. Moreover, FIG.4B shows the processing step of removing the cut surface 15 of the SiCbare wafer 14 after the machining process. Furthermore, FIG. 4C showsthe processing step of forming an oxide film on the principal surface 4of the SiC substrate 2 by applying an oxidation treatment to theprincipal surface 4 of the SiC substrate 2. Still further, FIG. 4D showsthe processing step of forming a SiC epitaxial growth layer 3 on the SiCsubstrate 2.

(a) Firstly, as shown in FIG. 4A, the hexagonal-crystal SiC ingot 13 isprepared. Subsequently, a plurality pieces of the SiC bare wafer 14 areobtained by cutting the SiC ingot 13 with the off angle θ of less than 4degrees in the [11-20] axis direction with respect to the (0001)surface. Next, the cut surface 15 ((0001) surface) of the SiC bare wafer14 is polished by a machining process, such as lap processing etc.(b) Subsequently, as shown in FIG. 4B, the cut surface 15 ((0001)surface) is removed by equal to or greater than approximately 500 nm,for example. As a removing method, Chemical Mechanical Polishing (CMP)technology, plasma etching technology, etc. are applicable, for example.Preferably, plasma etching may be applied. Although it is required forrelative long time for CMP with less damage to remove the surface byequal to or greater than 500 nm since the SiC is an extremely hardmaterial, the removing process will be completed in a short time, e.g.,approximately 20 minutes, if the plasma etching is used. Due to animprovement of polishing technique, it is possible to remove the damagedlayer in approximately 20 minutes per one wafer even if CMP is used, andtherefore the plasma etching or the CMP can appropriately be selected.On the other hand, with regard to the cut surface 15 of the SiC barewafer 14, the damage received by the plasma etching is small since theSiC is extremely hard. The damaged layer on the cut surface 15 of theSiC bare wafer 14 generated by the machining process after the cuttingprocess is sufficiently removed by the above-mentioned removing process,and thereby the SiC substrate 2 having a thickness t1 of approximately200 μm to approximately 500 μm is obtained.(c) Subsequently, as shown in FIG. 4C, an oxidation treatment is appliedon the principal surface 4 ((0001) surface) of the SiC substrate 2, andthereby the oxide film 16 is formed on the principal surface 4 of theSiC substrate 2. The oxidation treatment may be performed with a dryoxidation method or a wet oxidation method. Although illustration isomitted, the aforementioned oxide film 16 is formed also in a back sidesurface and a peripheral surface of the SiC substrate 2. Then, the oxidefilm 16 is removed using a fluoric acid (HF). By applying the formationprocess and the removing process of the oxide film 16, the damaged layerwhich cannot be removed by neither the CMP nor the plasma etching, andan altered layer (damaged layer) generated at the time of applying theCMP or plasma etching can be certainly removed from the cut surface 15of the SiC bare wafer 14. The formation process and the removing processfor the oxide film 16 may be performed only after the removing treatmentof the cut surface 15 by equal to or greater than 500-nm thickness, butalso only before the removing treatment or also before and after theremoving treatment.(d) Subsequently, as shown in FIG. 4D, the SiC epitaxial growth layer 3is crystal-grown on the SiC substrate 2 having the off angle of lessthan 4 degrees.

As materials, SiH₄ and C₃F₈ are supplied thereto, for example. SiH₄ andC₃F₈ are respectively diluted with H₂ gas, and then are supplied intothe reactor.

The epitaxial growth temperature may be within a range of approximately1630° C. to approximately 1690° C., for example, and may properly beapproximately 1680° C.

As a result of inspecting the epitaxially grown wafer surface, asurface-roughness defect density containing particles on the wafer wasequal to or less than 0.07 cm⁻². Namely, only approximately ten defectsare generated on a 150 mm wafer, and thereby a high quality wafer withfew surface unevenness defects can be obtained.

Moreover, the growth surfaces may be the c surface, the (11-20) surface,or the (10-10) surface.

6H—SiC can also be used therefor instead of 4H—SiC. The wafer is heatedat a temperature within a range of 1630° C. to 1690° C., and the C₃H₈diluted with hydrogen is supplied into the reactor, in order to performthe SiC homoepitaxial growth. SiHF₃ can also be used for materialsinstead of SiH₄.

FIG. 5 shows an example of a photograph of a hexagonal-crystal SiC ingotfrom which a SiC epitaxial wafer is cut. A length of bulk crystal of thehexagonal-crystal SiC ingot is approximately 30 mm.

FIG. 6A shows as schematic explanation of an example of cutting a SiCepitaxial wafer from the SiC ingot at an off angle of 4 degrees, as acomparative example. FIG. 6B shows a schematic explanation of an exampleof cutting a SiC epitaxial wafer from the SiC ingot at an off angle oftwo degrees.

The number of the SiC epitaxial wafers to be cut at the off angle of 4degrees is 39, and the number of the SiC epitaxial wafers to be cut atthe off angle of 2 degrees is 49, and thereby the number of the obtainedwafers to be cut at the off angle of 2 degrees is increased byapproximately 25%, where a thickness of a 6-inch φ wafer is 0.5 mm and alength of the bulk crystal is 30 mm. An occupied height L4 of the SiCepitaxial wafer to be cut at the off angle 4 of degrees is approximately19.4 mm, in the bulk crystal having the length of 30 mm. On the otherhand, an occupied height L2 of the SiC epitaxial wafer to be cut at theoff angle 2 of degrees is approximately 24.6 mm.

Accordingly, wafer costs can be reduced by reducing the off angle of thesubstrate.

(Yield Curve)

FIG. 7 shows a relationship between yield Y (%) and a device side length(mm) of a square-shaped device, using a defect density (cm⁻²) as aparameter.

In the case of the defect density is 0.2 count/cm², for example, if aSiC device of which the device side length is 10 mm is assumed, yieldequal to or greater than 80% can be expected, and if a SiC device ofwhich the device side length is 5 mm is assumed, yield equal to orgreater than 95% can be expected.

On the one hand, in the case of an acceptable value of the defectdensity being equal to or less than 0.5 count/cm², yield is equal to orgreater than 60% if a SiC device of which the device side length is 10mm is assumed, but yield equal to or greater than 85% can be expected ifa SiC device of which the device side length is 5 mm is assumed.

On the other hand, in the case of an acceptable value of the defectdensity being equal to or less than 1 count/cm², yield is equal to orgreater than 35% if a SiC device of which the device side length is 10mm is assumed, but yield equal to or greater than 75% can be expected ifa SiC device of which the device side length is 5 mm is assumed.

(Conversion from BPD to TED and Off Angle of Substrate)

FIG. 8A shows an explanation of an aspect of a conversion from a BasalPlane Dislocation (BPD) to a Threading Edge Dislocation (TED), in a casewhere an off angle is relatively large when forming the SiC epitaxialgrowth layer on the low-off angle SiC substrate 2. FIG. 8B shows anexplanation of an aspect of a conversion from the BPD to the TED, in acase where an off angle is relatively small.

A mechanism of increasing conversion probability from the basal planedislocation (BPD) to the threading edge dislocation (TED) in the Sicepitaxial growth layer is as follows.

The BPD is extended in parallel to a c-plane (0001) of the SiC crystalin the hexagonal crystal structure, and the TED is extended in adirection vertically to the c-plane (0001).

SiC epitaxial growth by a Chemical Vapor Deposition (CVD) methodadvances by a step flow growth on the SiC substrate provided with an offangle.

When the SiC epitaxial growth layer is formed, the dislocation istransmitted to be extended from the SiC substrate to the SiC epitaxialgrowth layer, but the TED extended substantially to a layer thicknessdirection becomes shorter than the BPD extended substantially to bevertical to the layer thickness direction.

Since an energy of the TED of which a dislocation introduction(development) is short becomes small as the energy of the dislocationintroduction (development) at the time of increasing the layer thicknessof the SiC epitaxial growth layer, the BPD is easily converted into theTED.

An effect of the BPD being converted into the TED, it is more remarkableas the off angle to become small. If the off angle is varied from 4degrees to 2 degrees, the length of the BPD to be extended by the SiCepitaxial growth becomes approximately twice as shown with the dashedline arrows in FIGS. 8A and 8B, and an energy difference in the case ofbeing converted into the TED becomes large. Since the length of the BPDwhen not being converted becomes long and the energy difference of thedislocation introduction (decompression) between the TED and the BPDbecomes large, if the off angle becomes small in particular, aconversion probability of the BPD to the TED becomes high.

For example, the conversion probability from the BPD to the TED when thelayer thickness of the SiC epitaxial growth layer is 10 μm is 99.26% ina substrate having the off angle of 4 degrees, but is 99.97% in asubstrate having the off angle of 1 degree.

According to the embodiments, there can be provided the high-quality SiCepitaxial wafer excellent in film thickness uniformity and uniformity ofcarrier density, having the small number of surface defects, and capableof reducing costs, also in low-off angle SiC substrates on SiC epitaxialgrowth.

According to the embodiments, it is possible to realize the SiCepitaxial growth capable of satisfying: excellent surface morphologyequivalent to a SiC epitaxial growth layer formed on the substratehaving the off angle of 4 degrees; uniformity of in-plane carrierdensity of a practical use level; and low defect density, in the SiCepitaxial growth layer formed on the 6-inch φ substrate having the offangle of 2 degrees.

The number of simultaneous processed wafers in the experiment isapproximately three wafers, which are equivalent to 150 Φ mm (wafers.The number of the processed wafers can be further increased by applyingfirst to fourth CVD apparatuses, mentioned below.

A layer thickness of a SiC epitaxial growth layer formed on thesubstrate having the off angle of 2 degrees is approximately 10.2 μm,for example.

Although a growth rate is a maximum of 40 μm/h in the SiC epitaxialgrowth layer formed on the substrate having the off angle of 4 degrees,a growth rate is approximately 9.8 μm/h, for example, in the SiCepitaxial growth layer formed on the substrate having the off angle of 2degrees.

The film thickness uniformity can be approximately 1.2% in the SiCepitaxial growth layer formed on the substrate having the off angle of 2degrees.

Doping concentration is approximately 1.5×10¹⁶ cm⁻³ in the SiC epitaxialgrowth layer formed on the substrate having the off angle of 4 degrees.On the other hand, the doping concentration can be approximately1.0×10¹⁶ cm⁻³ in the SiC epitaxial growth layer formed on the substratehaving the off angle of 2 degrees.

Uniformity of in-plane carrier density (σ/mean) is equal to or less thanapproximately 10% in the SiC epitaxial growth layer formed on thesubstrate having the off angle of 4 degrees. On the other hand, theuniformity thereof is equal to or less than approximately 7.0% in theSiC epitaxial growth layer formed on the substrate having the off angleof 2 degrees.

In the SiC epitaxial growth layer formed on the substrate having the offangle of 2 degrees, the uniformity of in-plane carrier densityequivalent to that of the SiC epitaxial growth layer formed on thesubstrate having the off angle of 4 degrees can be obtained, keeping amorphology of the same degree as that of the SiC epitaxial growth layerformed on the substrate having the off angle of 4 degrees, up to thethickness of the epitaxial growth layer of approximately 10 μm.

Defect density (CANDELA) is 0.40 count/cm² in the SiC epitaxial growthlayer formed on the substrate having the off angle of 4 degrees, but canbe 0.16 count/cm² in the SiC epitaxial growth layer formed on thesubstrate having the off angle of 2 degrees.

Defect densities (SICA) is 0.69 count/cm² in the SiC epitaxial growthlayer formed on the substrate having the off angle of 4 degrees, but canbe 0.21 count/cm² in the SiC epitaxial growth layer formed on thesubstrate having the off angle of 2 degrees.

Carrot defect density is 0.44 count/cm² in the SiC epitaxial growthlayer formed on the substrate having the off angle of 4 degrees, but canbe 0.01 count/cm² in the SiC epitaxial growth layer formed on thesubstrate having the off angle of 2 degrees.

A result of reducing the surface defect density can be obtained byforming the substrate having the off angle of 2 degrees.

A conversion probability from the BPD to the TED in the layer thicknessof 10 μm is within a range of 99.3 to 99.7% in the SiC epitaxial growthlayer formed on the substrate having the off angle of 4 degrees, but canbe within a range of 99.4% to 100% in the SiC epitaxial growth layerformed on the substrate having the off angle of 2 degrees. In thiscontext, the defect density (CANDELA) is a defect density detected by awafer surface inspection apparatus CANDELA made by KLA-TencorCorporation. The CANDELA is configured to scan a laser light on a wafersurface, and detects particles and crystal defects on the wafer surfacefrom a scattered light on the wafer surface.

The defect density (SICA) is a defect density detected by a wafersurface inspection apparatus SICA made by Lasertec Corporation. The SICAis capable of observing concavity and convexity in nanometer order onthe surface of the SiC epitaxial growth layer by a confocal differentialinterference optical system. It is also possible to detect large stepbunching and an epitaxial surface pit due to threading dislocation onthe surface of the SiC epitaxial growth layer which affect reliabilityof SiC-MOS devices.

Moreover, an experimental result of reducing the carrot defect densityhas been confirmed if the off angle is changed from 4 degrees to 4degrees. A mechanism thereof is as follows.

Although the carrot defect is a defect which grows up in a down stepdirection at the time of the epitaxial growth, with the threading screwdislocation (TSD) as a starting point, a length of the carrot defectoccurring at the time of growing up the layer thickness of the epitaxialgrowth layer becomes long if the substrate off angle becomes small. Ifthe off angle is changed from 4 degrees to 4 degrees, the length of thecarrot defect becomes approximately twice. This has affected a magnituderelationship between an energy change due to an introduction of thecarrot defect and an energy change in a case of being as in the TSDwithout occurrence of a carrot defect. As a result, if the off angle ischanged from 4 degrees to 2 degrees, the carrot defect density isreduced.

(Epitaxial Growth Apparatus)

FIG. 9A shows a schematic cross-sectional structure in a gas flowchannel direction showing an epitaxial growth apparatus 200 applied whenforming the SiC epitaxial growth layer on the low-off angle SiCsubstrate according to the embodiments, and FIG. 9B shows a schematiccross-sectional structure in a direction vertical to the gas flowchannel.

As shown in FIGS. 9A and 9B, the epitaxial growth apparatus 200according to the embodiments includes a gas injection port 140, a gasexhaust port 160, a heating unit 100, and a reactor. A material gascontains an Si compound used as a supply source of Si, and Carbon (C)compound used as a supply source of Carbon (C). The uniformity ofcarrier density may be less than 10%, and the defect density may be lessthan 1 count/cm²; and a C/Si ratio between the Si compound and theCarbon (C) compound is within a range of 0.7 to 0.95.

As shown in FIG. 9A and FIG. 9B, the reactor includes a horizontal-typereactor, and a plurality pieces of the SiC epitaxial wafers 1 can bearranged in a face up manner in the horizontal-type reactor.

An induction heating method using a coil is adopted as a heating methodof the heating unit 100.

The heating unit 100 is disposed via thermal insulation 112.

The SiC epitaxial wafers 1 are disposed on a holder plate 118 disposedbetween fixed susceptors 114. The holder plate 118 is disposed so as tobe rotatable on a rotating susceptor 116 connected to arotating-susceptor supporting base 125.

The fixed susceptor 114 and the rotating susceptor 116 are composed byincluding a structural member made from carbon. The structural membermade from carbon generates heat, and the SiC epitaxial wafers 1 areheated by being contacted with the structural member made from carbonvia the holder plate 118, or the SiC epitaxial wafers 1 are heated by aheated radiation from the structural member made from carbon. The holderplate 118 and the rotating-susceptor supporting base 125 can be composedby including a structural member made from stainless steel or astructural member made from carbon.

The epitaxial growth apparatus 200 according to the embodiments cansimultaneously mount 3×150 mm, i.e., three 6 inch φ wafers.

FIG. 10 shows a schematic plane configuration of arranging two 3-inchwafers in parallel in a 6-inch wafer pocket 6P on the holder plate 118at the time of the epitaxial growth, in the epitaxial growth apparatus200 according to the embodiments. In the epitaxial growth apparatus usedfor the experiment, as shown in FIG. 10, two 3-inch wafers are arrangedin parallel in the 6-inch wafer pocket 6P.

An apparatus configuration, operating conditions, a gas system, areaction system, etc., of the epitaxial growth applied to the experimentare as follows.

The epitaxial growth apparatus which is used therefor is an inductionheating type horizontal hot wall CVD apparatus (Probus-SiC (R) made byTokyo Electron Limited).

The gas used therefor includes SiH₄ (monosilane) used as Si material,C₃H₈ (propane) used as C material, N₂ (nitrogen) used as an n typedopant, and H₂ (hydrogen) used as carrier gas.

As fundamental growth conditions, a growth temperature T_(g) is within arange of 1620° C. to 1725° C., a growth pressure P is within a range of2 kPa to 11 kPa, a flow rate of H₂ carrier gas is within a range of 100slm to 150 slm. As typical values for the growth conditions, the growthtemperature T_(g) is 1680° C., the growth pressure P is 10.3 kPa, andthe flow rate of H₂ carrier gas is 120 slm.

The growth temperature T_(g) is changed within a range of 1620° C. to1725° C., the C/Si ratio of the material gas is changed within a rangeof 0.7 to 1.0, and the growth pressure P and the flow rate of H₂ carriergas are applied as the growth parameter.

Surface morphology including the defect density is observed through aconfocal differential interference microscope.

The film thickness uniformity of the epitaxial growth layer is measuredusing a Fourier transform infrared spectrometer (FT-IR).

Moreover, the doping uniformity of the epitaxial growth layer ismeasured using a mercury probe C-V system.

(Surface Morphology Limit of Relationship Between Growth Temperature andC/Si Ratio)

FIG. 11 shows a diagram of comparing a surface morphology limit betweenthe off angle of 4 degrees and the off angle of 2 degrees, in arelationship between a growth temperature and a C/Si ratio of materialgas showing satisfactory surface flatness when forming the SiC epitaxialgrowth layer on the SiC substrate.

In order to form the SiC epitaxial growth layer on the SiC substratehaving the off angle of 2 degrees, a lower temperature and a lower C/Siratio are required compared with a case where a SiC epitaxial growthlayer is formed on the SiC substrate having an off angle of 4 degrees.

The substrate having the off angle of 4 degrees can be applied if thegrowth temperature is within a range of approximately 1630° C. toapproximately 1725° C. and the C/Si ratio is within a range ofapproximately 0.7 to approximately 1.35.

On the other hand, the substrate having the off angle of 2 degrees canbe applied if the growth temperature is within a range of approximately1630° C. to approximately 1690° C. and the C/Si ratio is within a rangeof approximately 0.7 to approximately 0.95. In FIG. 11, the dashed lineAL shows a lower limit of the C/Si ratio of the material gas on theapparatus structure.

(Surface Morphology)

In images of confocal differential interference microscope of the SiCepitaxial growth layer formed on the SiC substrate having the off angleof 2 degrees shown in FIG. 11: FIG. 12A shows surface morphology in acase where the growth temperature T_(g) is 1680° C., the C/Si ratio is0.8, and a HAZE value is 5.7; FIG. 12B shows surface morphology in acase where the growth temperature T_(g) is 1680° C., the C/Si ratio is0.9, and a HAZE value is 5.9; FIG. 12C shows surface morphology in acase where the growth temperature T_(g) is 1650° C., the C/Si ratio is0.7, and a HAZE value is 5.5; FIG. 12D shows surface morphology in acase where the growth temperature T_(g) is 1650° C., the C/Si ratio is0.8, and a HAZE value is 5.5; and FIG. 12E shows surface morphology in acase where the growth temperature T_(g) is 1650° C., the C/Si ratio is0.9, and a HAZE value is 5.7. The results of FIGS. 12A to 12E areresults of each forming approximately 5-μm SiC epitaxial growth layerwithout a buffer layer on the SiC substrate having the off angle of 2degrees. The HAZE value is a surface roughness index by a surfaceinspection apparatus SICA6X. A photographic field is 750×750 μm² in eachcase.

Similarly, in images of confocal differential interference microscope ofthe SiC epitaxial growth layer formed on the SiC substrate having theoff angle of 4 degrees shown in FIG. 11: FIG. 13A shows surfacemorphology in a case where the growth temperature T_(g) is 1710° C., theC/Si ratio is 0.8, and a HAZE value is 19.7; FIG. 13B shows surfacemorphology in a case where the growth temperature T_(g) is 1710° C., theC/Si ratio is 1.0, and a HAZE value is 27.7; FIG. 13C shows surfacemorphology in a case where the growth temperature T_(g) is 1680° C., theC/Si ratio is 1.0, and a HAZE value is 14.1; and FIG. 13D shows surfacemorphology in a case where the growth temperature T_(g) is 1650° C., theC/Si ratio is 1.0, and a HAZE value is 15.1. The results of FIGS. 13A to13D are results of each forming approximately 5-μm SiC epitaxial growthlayer without a buffer layer on the SiC substrate having the off angleof 4 degrees. A photographic field is 750×750 μm² in each case.

In the SiC epitaxial growth layer formed on the SiC substrate having anoff angle of 4 degrees, as shown in FIG. 13, a relative large stepbunching has occurred if the C/Si ratio is equal to or greater than 1.0and the growth temperature T_(g) is equal to or greater than 1710° C.

On the other hand, in the SiC epitaxial growth layer formed on the SiCsubstrate having the off angle of 2 degrees, as shown in FIG. 12,occurrence of a relative large step bunching can be suppressed. Forexample, occurrence of a relative large step bunching can be suppressedif the C/Si ratio is equal to or less than approximately 0.95 and thegrowth temperature T_(g) is equal to or less than 1690° C., for example.

(Dependency of Growth Pressure)

FIG. 14 shows dependency of growth pressure P (kPa) of a triangulardefect density (cm⁻²) and uniformity (a/mean) (%) of a carrier density(N_(D)-N_(A)) (120 slm-H₂, C/Si ratio=0.9), in a result of forming theSiC epitaxial growth layer on the SiC substrate having the off angle of2 degrees according to the embodiments.

The triangular defect density (cm⁻²)<approximately 1 (cm⁻²) is satisfiedif the growth pressure of the SiC epitaxial growth layer is within arange of 3 kPa to 11 kPa. Moreover, the carrier density (N_(D)-N_(A))uniformity (σ/mean) of less than 10(%) is satisfied if the growthpressure is equal to or greater than approximately 7.5 kPa.

(Dependency of Flow Rate of Carrier Gas)

FIG. 15 shows dependency of flow rate of carrier gas (H₂ gas flow) (slm)of a triangular defect density (cm⁻²) and uniformity (a/mean) (%) of acarrier density (N_(D)-N_(A)) (the C/Si ratio=0.9, the growth pressureP=10.3 kPa), in a result of forming the SiC epitaxial growth layer onthe SiC substrate having the off angle of 2 degrees according to theembodiments.

The triangular defect density (cm⁻²)<approximately 1 (cm⁻²) is satisfiedif the flow rate of the carrier gas at the time of forming the SiCepitaxial growth layer is within a range of 100 slm to 150 slm.Moreover, the carrier density (N_(D)-N_(A)) uniformity (c/mean) of lessthan 10(%) is satisfied if the flow rate of the carrier gas is within arange of 100 slm to 120 slm.

In the SiC epitaxial growth layer formed on the SiC substrate having theoff angle of 2 degrees according to the embodiments, an effect of thegrowth parameter (the growth pressure P (kPa), the flow rate of carriergas (H₂ gas flow) (slm)) to the triangular defect density (cm⁻²) and thecarrier density (N_(D)-N_(A)) uniformity (σ/mean) (%) shows a tendencysimilar to that of the SiC epitaxial growth layer formed on the SiCsubstrate having an off angle of 4 degrees.

(Process Window)

An effect of the growth parameter to the surface morphology, the defectdensity, and the uniformity of in-epitaxial-plane carrier density(σ/mean) is carefully examined, and thereby a process window of the SiCepitaxial growth to the Si surface side of the SiC substrate having theoff angle of 2 degrees is derived.

FIG. 16 shows an explanation of the process window in a relationshipbetween the growth temperature T_(g) (° C.) and the C/Si ratio under thegrowth pressure P=10.3 (kPa), in a result of forming the SiC epitaxialgrowth layer on the SiC substrate having the off angle of 2 degreesaccording to the embodiments.

In FIG. 16, a surface morphology limit of the SiC substrate having theoff angle of 2 degrees is within a range shown with the dashed line,i.e., the growth temperature T_(g) (° C.) being within a range ofapproximately 1630° C. to approximately 1690° C., and the C/Si ratiobeing within a range of approximately 0.7 to approximately 0.95.

On the other hand, a range of satisfying the triangular defect density<1count/cm² is within the range shown with the hatched region T in FIG.16.

Moreover, a range of satisfying the carrier density (N_(D)-N_(A))uniformity (σ/mean) (%)<10% is within the range shown with the hatchedregion U in FIG. 16.

Accordingly, a region of satisfying all of the surface morphology limit,the triangular defect density<1 count/cm², and the carrier density(N_(D)-N_(A)) uniformity (σ/mean) (%)<10% is the overlapped region (T+U)between the hatched region T and the hatched region U.

For example, the black circle plot ○ PD represented with the growthtemperature T_(g) (° C.)=1680° C. and the C/Si ratio=0.9 under thegrowth pressure P=10.3 (kPa) corresponds to an example of conditions ofsatisfying all of the surface morphology limit, the triangular defectdensity<1 count/cm², and the carrier density (N_(D)-N_(A)) uniformity(σ/mean) (%)<10%, as a result of forming the SiC epitaxial growth layeron the SiC substrate having the off angle of 2 degrees according to theembodiments.

In this context, the (N_(D)-N_(A)) in the carrier density (N_(D)-N_(A))uniformity (σ/mean) (%) shows the carrier density (a difference betweendonor concentration and acceptor concentration) measured by acapacitance-voltage measurement (C-V measurement). The vertical axis inFIGS. 14, 15, and 17 indicates uniformity (σ/mean) of the value(N_(D)-N_(A)) obtained by performing the C-V measurement with respect tothe entire wafer surface.

(Dependency of C/Si Ratio)

FIG. 17 shows dependency of C/Si ratio of the defect density (cm⁻²) andthe uniformity (%) of carrier density (N_(D)-N_(A)) (the growthtemperature T_(g)=1680° C., the flow rate of carrier gas 120 slm-H₂, thegrowth pressure P=10.3 (kPa)), in a result of forming the SiC epitaxialgrowth layer on the SiC substrate having the off angle of 2 degreesaccording to the embodiments.

As shown in FIG. 17, a morphology limit from which the surface flatnessbecomes satisfactory is a case where the value of the C/Si ratio isequal to or less than 0.95. On the other hand, if the value of the C/Siratio is within a range of approximately 0.7 to approximately 0.95, thedefect density becomes less than 1 (cm⁻²). If the value of the C/Siratio is within a range of approximately 0.7 to approximately 0.85, thedefect density becomes less than 0.5 (cm⁻²). Moreover, if the value ofthe C/Si ratio is within a range of approximately 0.85 to approximately0.95, the carrier density (N_(D)-N_(A)) uniformity becomes less than10(%).

In order to form the SiC epitaxial growth layer on the SiC substratehaving the off angle of 2 degrees, a lower temperature and a lower C/Siratio are required compared with a case where a SiC epitaxial growthlayer is formed on the SiC substrate having an off angle of 4 degrees.On the other hand, it is known that occurrence of the triangular defectcan be suppressed under a relative high growth temperature T_(g).Accordingly, although there is a danger of increasing the probability ofoccurrence of the triangular defect if reducing the growth temperature,the triangular defect density can be reduced by setting a relatively lowC/Si ratio under a relative high growth temperature T_(g)=1680° C. andrelatively high growth pressure P=10.3 kPa, as shown in FIG. 17.

It is confirmed from an observation result of surface morphology that asurface flatness of the same degree as that of the substrate having anoff angle of 4 degrees can be realized if the C/Si ratio is equal to orless than 0.9.

However, if the C/Si ratio becomes relative low, a tendency for theuniformity of carrier density (%) to deteriorate rapidly is observed, asshown in FIG. 17. The results show that the triangular defect densityand the uniformity of carrier density (%) reflecting the surfacemorphology have a tradeoff relationship with respect to the growthparameter (the C/Si ratio, the growth pressure P, and the flow rate ofcarrier gas). By paying attention to a starting point of occurrence ofthe triangular defect, such a tradeoff relationship can be canceled.

The triangular defect is a generic name for defects having a triangularshape by wafer surface observation in defects to be extended to a downstep direction in the SiC epitaxial growth layer.

The triangular defect corresponds to: 3C-inclusion to be extended as astarting point with particles on the wafer or downfall particles comingfrom a furnace wall of a CVD apparatus to be adhered thereto; anddefects in which triangular-shaped surface morphology is observed instacking faults on the basis of dislocation of the wafer.

—Downfall—

As defects which occurs when the SiC epitaxial growth layer is formed onthe SiC substrate having the off angle of 2 degrees, an example ofdownfall is illustrated as shown in FIG. 18A, another example of thedownfall is illustrated as shown in FIG. 18B, still another example ofthe downfall is illustrated as shown in FIG. 18C, yet another example ofthe downfall is illustrated as shown in FIG. 18D, further example of thedownfall is illustrated as shown in FIG. 18E, and still further otherexample of the downfall is illustrated as shown in FIG. 18F.

The downfall formed as a starting point with particles on the SiCsubstrate having the off angle of 2 degrees or downfall particles comingfrom the furnace wall of the CVD apparatus to be adhered thereto has anapproximate circle shape approximately measuring several μm to severaltens of μm in diameter, as shown in FIGS. 18A to 18F.

—Carrot—

As defects which occurs when the SiC epitaxial growth layer is formed onthe SiC substrate having the off angle of 2 degrees, an example of acarrot defect is illustrated as shown in FIG. 19A, another example ofthe carrot defect is shown as shown in FIG. 19B, still another exampleof the carrot defect is illustrated as shown in FIG. 19C, and yetanother example of the carrot defect is illustrated as shown in FIG.19D.

Although the length of the carrot defect is dependent on the layerthickness of the epitaxial growth layer, it is proved that the lengththereof can be equal to or greater than approximately 100 μm, as shownin FIGS. 19A to 19D.

—Triangular Defect—

As defects which occurs when the SiC epitaxial growth layer is formed onthe SiC substrate having the off angle of 2 degrees, an example of atriangular defect is illustrated as shown in FIG. 20A, another exampleof the triangular defect is illustrated as shown in FIG. 20B, stillanother example of the triangular defect is illustrated as shown in FIG.20C, and yet another example of the triangular defect is illustrated asshown in FIG. 20D.

Although the size of the triangular defect is determined in accordancewith the layer thickness of the epitaxial growth layer grown-up afterthe occurrence of defect, it is proves that a length of one side of thetriangular shape composing the triangular defect can be equal to orgreater than approximately 100 μm, as shown in FIGS. 20A to 20D. Inaddition, a relationship between the size of the triangular defect andthe layer thickness of the epitaxial growth layer is as explained inFIG. 22.

—Downfall and Triangular Defect—

As defects which occurs when the SiC epitaxial growth layer is formed onthe SiC substrate having the off angle of 2 degrees, an example ofdownfall and triangular defect is illustrated as shown in FIG. 21A, andanother example of the downfall and triangular defect is illustrated asshown in FIG. 21B.

As shown in FIGS. 21A and 21B, it is proved that the triangular defectcan occur as a starting point with the downfall.

As a detail of the defects of the SiC epitaxial growth on the substratehaving the off angle of 2 degrees, the triangular defect account forapproximately 80%, the carrot defect account for approximately 10%, andthe downfall defect account for approximately 10%. The aforementionedvalues are average values of five wafers obtained by SiC epitaxialgrowth on 3-inch p wafer of the substrate having the off angle of 2degrees.

(Occurrence Mechanism of Triangular Defect)

FIG. 22A is a schematic plain diagram showing a triangular defectexample, in an explanatory diagram showing an occurrence mechanism ofthe triangular defect which occurs when the SiC epitaxial growth layeris formed on the SiC substrate having the off angle θ. Moreover, FIG.22B shows a schematic cross-sectional diagram of the triangular defect.

As shown in FIGS. 22A and 22B, if there is a foreign substance whichbecomes inhibition of step flow growth at a starting point A, a crystallaminated structure which is different from the substrate is radiallyextended with step flow growth, as shown with the lines B and C.

A thickness of the epitaxial growth layer can be computed on the basisof the length of the triangular defect along in a direction of the stepflow. More specifically, the layer thickness of the SiC epitaxial growthlayer at the time of occurrence of defect can be estimated on the basisof an expansion width in the down step direction of the surfacetriangular defect.

On the basis of a relationship between the expansion width L and offangle θ in the down step direction, and the layer thickness d of the SiCepitaxial growth layer, the layer thickness D_(d) of the SiC epitaxialgrowth layer at the time of the occurrence of defect is expressed by thefollowing equation (1):D _(d) =d−L×tan θ  (1)The expansion width L in the down step direction can be measured from atriangular defect image obtained by SICA, regular observation throughoptical microscope, etc. Accordingly, the layer thickness D_(d) of theSiC epitaxial growth layer at the time of the occurrence of defect canbe nondestructively estimated by measuring the expansion width L in thedown step direction.(Reduction Measures Against Triangular Defect)

FIG. 23 shows an explanatory diagram of reduction measures of atriangular defect occurring when the SiC epitaxial growth layer 3 isformed on the low-off angle SiC substrate 2.

If the C/Si ratio is relative high, two Dimensional Nucleation (2DN)growing up becomes active in a growth mode, and uniformity of carrierdensity is also improved, as shown in FIG. 23. On the other hand, if theC/Si ratio is relative low, step flow growth becomes active in thegrowth mode, and the uniformity of carrier density also becomes adeteriorating tendency.

Approximately 80% or more of the defects in the triangular defectdensities have occurred near an interface between the low-off angle SiCsubstrate (2) and the SiC epitaxial growth layer (3).

It is necessary to remove an inhibition factor of the step flow asreduction measures against the triangular defect. Countermeasure againstthe foreign substances as an inhibition factor of the step flow is tothoroughly perform wafer cleaning. Moreover, countermeasures against thedislocation are to optimize hydrogen etching conditions before the SiCepitaxial growth and to optimize wafer polishing conditions.

Furthermore, the C/Si ratio is set to be low and the buffer layer 3B inwhich the defect density is reduced is formed at an initial stage forforming the SiC epitaxial growth layer 3 on the low-off angle SiCsubstrate 2, and then, a drift layer 3D is formed on the buffer layer 3Bunder growth conditions of relative high C/Si ratio. Thereby, the SiCepitaxial wafer 1 having satisfactory uniformity of carrier density canbe provided.

FIG. 24 shows a diagram of a relationship between a probability ofoccurrence (%) of a triangular defect and a thickness of the epitaxialgrowth layer 3, in a result of forming the SiC epitaxial growth layer 3on the SiC substrate 3 having the off angle of 2 degrees according tothe embodiments. The number N of the triangular defects counted in thiscase is 61.

As a probability of occurrence (%) of the triangular defects, 80% ormore of the triangular defects has occurred near the interface betweenthe SiC substrate and the SiC epitaxial growth layer, as shown in FIG.24. More specifically, before the thickness of the SiC epitaxial growthlayer is reached at approximately 0.25 μm, 80% or more of the triangulardefects have occurred. This is based on a result of measuring three3-inch φ wafers.

On the basis of the above-mentioned result, in order to suppress theoccurrence of the triangular defect, the buffer layer 3B is formed onthe SiC substrate having the off angle of 2 degrees 2, under growthconditions of the relative low C/Si ratio, as shown in FIG. 17, andthen, a drift layer 3D is formed on the buffer layer 3B under growthconditions of relative high C/Si ratio. Thereby, the SiC epitaxial wafer1 having satisfactory uniformity of carrier density can be provided.There can be provided the SiC epitaxial wafer 1: capable of reducingoccurrence of such step bunching or a triangular defect density;excellent in film thickness uniformity and uniformity of carrier densityin a tradeoff relationship with the reduction of the defect density; andcapable of reducing the costs by the SiC substrate having the off angleof 2 degrees 2.

In results of forming the SiC epitaxial growth layer 3 on the SiCsubstrate having the off angle of 2 degrees 2 according to theembodiments, a defect density map on a 3-inch p wafer (inside) arrangedside by side in a 6 inch c wafer pocket is illustrated as shown in FIG.25A, and a defect density map on the 3 inch φ wafer (outside) arrangedside by side in the 6 inch φ wafer pocket is illustrated as shown inFIG. 25B. The results shown in FIGS. 25A and 25B correspond to astructure in which the buffer layer is not applied, as shown in FIG. 26.In this context, the C/Si ratio in the SiC epitaxial growth is 0.9. Eachthickness of the SiC epitaxial growth layers 3 is approximately 10 μm.The points (black circle plots ●) in FIGS. 25A and 25B respectivelyindicate positions of the detected defects (triangular defects, carrotdefects, and downfall).

On the other hand, in results of forming the drift layer 3D via thebuffer layer 3B on the SiC substrate having the off angle of 2 degrees 2according to the embodiments, a defect density map on the 3 inch φ wafer(inside) arranged side by side in the 6 inch φ wafer pocket isillustrated as shown in FIG. 25C, and a defect density map on the 3 inchφ wafer (outside) arranged side by side in the 6 inch φ wafer pocket isillustrated as shown in FIG. 25D. The results shown in FIGS. 25A and 25Bcorrespond to a structure in which the buffer layer 3B is applied, asshown in FIG. 28A. In this case, the C/Si ratio in the SiC epitaxialgrowth of the buffer layer 3B is 0.75, and the C/Si ratio in the SiCepitaxial growth of the drift layer 3D is 0.9. Each thickness of thebuffer layer 3B and the drift layer 3D in the SiC epitaxial growth layer3 is approximately 10 μm. The points (black circle plots ●) in FIGS. 25Cand 25D respectively indicate positions of the detected defects(triangular defects, carrot defects, and downfall).

As proved from the above-mentioned results, the defect density isapproximately 0.60 count/cm² to the structure in which the buffer layer3B is not applied, but the defect density is approximately 0.21count/cm² in the structure to which the buffer layer 3B is applied. Theoccurrence of the defects can be suppressed by forming the buffer layer3B having the low C/Si ratio at the initial stage when the SiC epitaxialgrowth layer 3 is formed on the SiC substrate having the off angle of 2degrees 2.

Moreover, the film thickness uniformity of 1.2% and the uniformity ofthe carrier density (σ/mean) of 7% can be obtained at a growth rate ofapproximately 10 μm/h, in the SiC epitaxial growth on the SiC substratehaving the off angle of 2 degrees, in the structure to which the bufferlayer is applied.

Moreover, a defect-free chip yield of the SiC epitaxial growth layer 3is approximately 86% in 5 mm square, and is approximately 55% in 10 mmsquare, before applying the reduction measures of defects (FIGS. 25A and25B). On the other hand, the yield is improved to approximately 95% at 5mm square and is improved to approximately 81% in 10 mm square, afterapplying the reduction measures of defects (FIGS. 25C and 25D).

FIG. 26 shows a schematic structure example of not including the bufferlayer 3B in the SiC epitaxial growth layer 3 formed on the SiC substrate2 having the off angle of 2 degrees according to the embodiments. Inthis case, the SiC substrate 2 is a 4H—SiC substrate, and the epitaxialgrowth is already applied on the (0001) surface thereof. Moreover, thegrowth temperature T_(g) is 1670° C., the C/Si ratio is 0.9, the growthpressure P is 6.3 (kPa), and the thickness of the SiC epitaxial growthlayer is 5 μm.

In addition, a holding time is changed in a water vapor atmosphere (10.6kPa, 1655° C.) before the SiC epitaxial growth is started. If the SiCsubstrate 2 is held in a low pressure atmosphere including hydrogen, theSiC substrate 2 is etched. The aforementioned step is performed in orderto remove adhered particles removing of the wafer surface or to remove aresidual damaged layer (high-density dislocation loop) after wafersurface polishing by etching.

FIG. 27 shows dependency of etching depth of a defect density (cm⁻²) anda reflection loss (a. u.), in a result of forming the SiC epitaxialgrowth layer 3 on the SiC substrate 2 having the off angle of 2 degreesaccording to the embodiments. As the defect density (cm⁻²), a triangulardefect density, a shallow pit density, and a bump density are measured.Moreover, the white circle plots ∘ indicate reflection loss.

A reason that the reflection loss is increased as the etching depth isincreased is as follows.

In the etching of SiC in the hydrogen atmosphere, the step of the wafersurface progresses so as to retreat, contrary to the step flow growth atthe time of the SiC epitaxial growth.

If uniform etching is inhibited due to particles of the wafer surface ordislocation of the wafer (including derivation from processed damage) inthat time, short step bunching occurs on a perimeter thereof.

The step bunching which occurs at the time of the etching is notdisappeared in the subsequent epitaxial growth, but is extended in avertical direction of the down step on the contrary.

If such a step bunching occurs with high density, the step bunching isoverlapping and thereby being observed as “surface roughness.”

If the etching depth is increased, a length of the short step bunchingwhich occurs due to nonuniformity of etching becomes long. This pointcan be explained similarly to the relationship between the occurrencedepth of the triangular defect and the thickness and off angle of theepitaxial growth layer.

The length of the step bunching of the substrate having a small offangle becomes longer also with the same etching depth.

The reflection loss in the SICA is an index indicating a degree ofscattering and reduction due to the surface roughness of a reflectedlight from the wafer surface at the time of observation through aconfocal differential interference microscope, etc. In SICA, a degree ofthe surface roughness derived from the step bunching can be detected,and is used as the index.

The surface roughness index HAZE obtained by the SICA is a name of thereflection loss in the inspection apparatus SICA.

(Need for Buffer Layer)

The buffer layer 3B is not necessary component, but the need therefor isdetermined on the basis of values of the morphology limit, theuniformity of carrier density, and the epitaxial defect density,required for the SiC epitaxial wafer 1.

In order to reduce the defect density, a low C/Si ratio of material gas(or low growth pressure P, a high flow rate of carrier gas (i.e.,conditions of reducing a practical C/Si ratio on the wafer surface)) issuitable. However, such growth conditions are used, in-plane uniformityof the carrier density is reduced as a trade-off.

In the case of the 2-degree off angle epitaxial growth, and using theconditions of in-plane uniformity of carrier density σ/mean<10%, if anacceptable value of the defect density is less than 1 count/cm², thebuffer layer 3B with the low C/Si ratio is needless. On the other hand,if the acceptable value of the defect density is less than 0.5count/cm², the buffer layer 3B with the low C/Si ratio is needed.

—Conditions of Buffer Layer—

Fundamental Requirements:

The buffer layer grows up under growth conditions where the layerthickness is equal to or greater than 0.5 μm and the practical C/Siratio is lower than that of the drift layer 3D (i.e., SiC epitaxialgrowth layer above the buffer layer 3B). In order to obtain a similarresult, the C/Si ratio of material gas may be reduced, the growthpressure P may be reduced, and the flow rate of carrier gas may beincreased.

—Other Requirements—

When the C/Si ratio at the time of the drift layer growth is 0.9, it ispreferable that the C/Si ratio of material gas at the time of formingthe buffer layer 3B is within a range of 0.6 to 0.9. It is morepreferable that the C/Si ratio of material gas at the time of formingthe buffer layer 3B is approximately 0.75. If the C/Si ratio of materialgas is equal to or less than 0.6, since the Si composition of an adheredfilm to the furnace wall of the CVD apparatus becomes high, a filmstress becomes large and thereby a furnace material is easily cracked.

—Layer Thickness of Buffer Layer—

If the layer thickness of the buffer layer 3B is formed thickly, thereduction effect of the defect density can be certainly obtained. On theother hand, since the thickness of drift layer 3D is determined inaccordance with a device breakdown voltage required, the total layerthickness of the epitaxial growth layer 3 becomes thick for the amountof the thickness of the buffer layer 3B.

From a balance between a process time duration of epitaxial growth andan increment of channel resistance at the time of the devicefabrication, and from a viewpoint of reproducibility of the reductioneffect of defects, a lower limit of the layer thickness of the bufferlayer 3B is approximately 0.5 μm.

—Doping to Buffer Layer—

A nitrogen (N) doping concentration to the buffer layer 3B is set morehighly than a nitrogen (N) doping concentration to the drift layer 3D inorder to suppress an increase in a channel resistance. In this case, thenitrogen (N) doping concentration to the buffer layer 3B is set as lessthan 4×10¹⁹ cm⁻³. This is because stacking faults easily occur, if thenitrogen (N) doping concentration to the buffer layer 3B becomes high.

(Relationship Between Thickness of Buffer Layer Having Low C/Si Ratioand Defect Density) FIG. 28A shows a schematic structure example of aresult of forming a drift layer 3D via the buffer layer 3B on the SiCsubstrate having the off angle of 2 degrees 2 according to theembodiments. In this case, the growth temperature T_(g) is 1680° C., thegrowth pressure P id 10.3 (kPa), the C/Si ratio of the buffer layer 3Bis 0.75, the thickness of the buffer layer 3B is X μm, the C/Si ratio ofthe drift layer 3D is 0.9, and the thickness of the drift layer 3D is 10μm.

FIG. 28B shows dependency of the defect density (cm⁻²) and the thicknessX (μm) of the buffer layers 3B (C/Si ratio of the buffer layer is 0.75),in a result of forming the drift layer 3D via the buffer layer 3B on theSiC substrate having the off angle of 2 degrees 2 according to theembodiments.

With regard to a layer thickness level of each buffer layer 3B, FIG. 28Bshows a variation range of measured results of six 3-inch φ wafers (fourwafers only when the thickness of the buffer layer 3B is 1.5 μm). Assurface defects of each drift layer 3D, the carrot defect density andthe triangular defect density are totaled to be measured. The downfalldensity is excepted since it is dependent on a device condition.

FIG. 29 shows A typical example of an image of confocal differentialinterference microscope (field of view: 750×750 μm²) of the drift layer3D formed via the buffer layer 3B on the SiC substrate having the offangle of 2 degrees 2. In this case, the growth temperature T_(g) is1680° C., the C/Si ratio of the buffer layer 3B is 0.75, the thickness Xof the buffer layer 3B is 0.5 μm, the C/Si ratio of the drift layer 3Dis 0.9, and the thickness of the drift layer 3D is 10 μm.

The defect density (the carrot defect density and the triangular defectdensity) of the drift layer 3D formed via the buffer layer 3B on the SiCsubstrate having the off angle of 2 degrees 2 is reduced as thethickness X of the buffer layer 3B is increased, and is reduced toapproximately 0.2 count/cm² if the thickness X is equal to or greaterthan 0.5 μm, for example.

As obvious from the relationship of the yield Y (%) and the device sidelength (mm) using the defect density (count(s)/cm²) as a parameter shownin FIG. 7, for example, in the case of the defect density is 0.2count/cm² if a SiC device of which the device side length is 10 mm isassumed, the yield equal to or greater than 80% can be expected, and ifa SiC device of which the device side length is 5 mm is assumed, yieldequal to or greater than 95% can be expected.

(First CVD Apparatus)

As shown in FIG. 30, a schematic configuration example of a first CVDapparatus applicable to the SiC epitaxial growth, in a manufacturingapparatus of the SiC epitaxial wafer according to the embodimentsincludes: a gas injection port 140; a gas exhaust port 160; a heatingunit 100; and a vertical-type reactor 120.

As a heating method of the heating unit 100, resistance heating,induction heating using a coil, lamp heating, etc. are adoptable. In thecase of the induction heating method, a structural member made fromcarbon (not shown in FIG. 14) disposed near the wafer, the structuralmember made from carbon produces heat, and then the wafer in contactwith the structural member is heated or the wafer is heated withradiation from the structural member made from carbon.

In the vertical-type reactor 120, a plurality pieces of the SiCepitaxial wafers 1 can be disposed in a face up manner or face downmanner.

While the material gas is supplied from the gas injection port 140 at alower portion of the vertical-type reactor 120 and then is exhaustedfrom the gas exhaust port 160 at an upper portion of the vertical-typereactor 120, the materials which flows on the surface of the pluralitypieces of the SiC epitaxial wafers 1 react, thereby forming the SiCepitaxial growth layer.

In this case, a material gas supplied when forming the SiC epitaxialgrowth layer on the substrate having the off angle of less than 4degrees contains an Si compound used as a supply source of Si, andCarbon (C) compound used as a supply source of Carbon (C). Theuniformity of carrier density may be less than 10%, and the defectdensity may be less than 1 count/cm²; and a C/Si ratio between the Sicompound and the Carbon (C) compound is within a range of 0.7 to 0.95.

Moreover, the SiC epitaxial growth layer may include a buffer layerdisposed on the substrate, and a drift layer disposed on the bufferlayer. In this context, uniformity of carrier density may be less than10% and a defect density is less than 0.5 count/cm²; and the C/Si ratioof the buffer layer 3B may be controlled to be lower than the C/Si ratioof the drift layer 3D.

The off angle may be 2 degrees.

Moreover, a growth temperature of the SiC epitaxial growth layer may bewithin a range of 1630° C. to 1690° C.

Moreover, a growth pressure of the SiC epitaxial growth layer may bewithin a range of 3 kPa to 11 kPa.

Moreover, a flow rate of carrier gas at the time of formation of the SiCepitaxial growth layer may be within a range of 100 slm to 150 slm.

The Si compound may contain any one material of SiH₄, SiH₃F, SiH₂F₂,SiHF₃, or SiF₄, for example. Other compounds containing chlorine (Cl)may be used as the Si compound.

Moreover, the C compound may contain any one material of CF₄, C₂F₆,C₃F₈, C₄F₆, C₄F₈, C₅F₈, CHF₃, CH₂F₂, CH₃F, or C₂HF₅. Other compoundscontaining chlorine (Cl) may be used as the C compound.

Moreover, the SiC epitaxial growth layer may contain any one material of4H—SiC, 6H—SiC, 2H—SiC, or 3C—SiC.

A diameter of the substrate 2 having an off angle of less than 4 may beequal to or greater than 100 mm, for example.

The substrate 2 having an off angle of less than 4 may contain 4H—SiC or6H—SiC. Moreover, any one BN, AlN, Al₂O₃, Ga₂O₃, diamond, carbon, orgraphite may be contained instead of the SiC.

In the SiC epitaxial growth for the SiC epitaxial wafer according to theembodiments, at least one of H₂, Ar, HCl, and the F₂ is applicable ascarrier gas.

As the materials for dopant, N (nitrogen) or TMA can be applied.

(Second CVD Apparatus)

As shown in FIG. 31, a schematic configuration example of a second CVDapparatus applicable to the SiC epitaxial growth, in a manufacturingapparatus of the SiC epitaxial wafer according to the embodimentsincludes: a gas injection port 140; a gas exhaust port 160; a heatingunit 100; and a vertical-type reactor 120.

As a heating method of the heating unit 100, resistance heating,induction heating using a coil, lamp heating, etc. are adoptable.

In the case of the induction heating method, a structural member madefrom carbon (not shown in FIG. 14) disposed near the wafer, thestructural member made from carbon produces heat, and then the wafer incontact with the structural member is heated or the wafer is heated withradiation from the structural member made from carbon.

In the vertical-type reactor 120, the plurality pieces of the SiCepitaxial wafers 1 are disposed so as to be parallel to the flow of thegas.

While the material gas is supplied from the gas injection port 140 at alower portion of the vertical-type reactor 120 and then is exhaustedfrom the gas exhaust port 160 at an upper portion of the vertical-typereactor 120, the materials which flows on the surface of the pluralitypieces of the SiC epitaxial wafers 1 react, thereby forming the SiCepitaxial growth layer.

In this case, a material gas supplied when forming the SiC epitaxialgrowth layer on the substrate having the off angle of less than 4degrees contains an Si compound used as a supply source of Si, andCarbon (C) compound used as a supply source of Carbon (C). Theuniformity of carrier density may be less than 10%, and the defectdensity may be less than 1 count/cm²; and a C/Si ratio between the Sicompound and the Carbon (C) compound is within a range of 0.7 to 0.95.

Moreover, the SiC epitaxial growth layer may include a buffer layerdisposed on the substrate, and a drift layer disposed on the bufferlayer. In this context, uniformity of carrier density may be less than10% and a defect density is less than 0.5 count/cm²; and the C/Si ratioof the buffer layer 3B may be controlled to be lower than the C/Si ratioof the drift layer 3D.

The off angle may be 2 degrees.

Moreover, a growth temperature of the SiC epitaxial growth layer may bewithin a range of 1630° C. to 1690° C.

Moreover, a growth pressure of the SiC epitaxial growth layer may bewithin a range of 3 kPa to 11 kPa.

Moreover, a flow rate of carrier gas at the time of formation of the SiCepitaxial growth layer may be within a range of 100 slm to 150 slm.

The Si compound may contain any one material of SiH₄, SiH₃F, SiH₂F₂,SiHF₃, or SiF₄, for example. Other compounds containing chlorine (Cl)may be used as the Si compound.

Moreover, the C compound may contain any one material of C₃H₈, C₂H₄,C₂H₂, CF₄, C₂F₆, C₃F₈, C₄F₆, C₄F₈, CsF₈, CHF₃, CH₂F₂, CH₃F, or C₂HF₅.Other compounds containing chlorine (Cl) may be used as the C compound.

Moreover, the SiC epitaxial growth layer may contain any one material of4H—SiC, 6H—SiC, 2H—SiC, or 3C—SiC.

A diameter of the substrate 2 having an off angle of less than 4 may beequal to or greater than 100 mm, for example.

The substrate 2 having an off angle of less than 4 may contain 4H—SiC or6H—SiC. Any one BN, AlN, Al₂O₃, Ga₂O₃, diamond, carbon, or graphite maybe contained instead of the SiC.

In the SiC epitaxial growth for the SiC epitaxial wafer according to theembodiments, at least one of H₂, Ar, HCl, and the F₂ is applicable ascarrier gas.

As the materials for dopant, N (Nitrogen) or TMA can be applied.

(Third CVD Apparatus)

As shown in FIG. 32, a schematic configuration example of a third CVDapparatus applicable to the SiC epitaxial growth, in a manufacturingapparatus 200 of the SiC epitaxial wafer according to the embodimentsincludes: a gas injection port 140; a gas exhaust port 160; a heatingunit 100; and a horizontal-type reactor 130.

As a heating method of the heating unit 100, resistance heating,induction heating using a coil, lamp heating, etc. are adoptable. In thecase of the induction heating method, a structural member made fromcarbon (not shown in FIG. 14) disposed near the wafer, the structuralmember made from carbon produces heat, and then the wafer in contactwith the structural member is heated or the wafer is heated withradiation from the structural member made from carbon.

In the horizontal-type reactor 130, the plurality pieces of the SiCepitaxial wafers 1 can be vertically arranged in the upward directionstand so as to be opposite to the flow of gas.

While the material gas is supplied from the gas injection port 140 ofthe horizontal-type reactor 130, passes through the plurality pieces ofthe SiC epitaxial wafers 1, and then is exhausted from the gas exhaustport 160, the materials which flows on the surface of the pluralitypieces of the SiC epitaxial wafers 1 react, thereby forming the SiCepitaxial growth layer.

In this case, a material gas supplied when forming the SiC epitaxialgrowth layer on the substrate having the off angle of less than 4degrees contains an Si compound used as a supply source of Si, andCarbon (C) compound used as a supply source of Carbon (C). Theuniformity of carrier density may be less than 10%, and the defectdensity may be less than 1 count/cm²; and a C/Si ratio between the Sicompound and the Carbon (C) compound is within a range of 0.7 to 0.95.

Moreover, the SiC epitaxial growth layer may include a buffer layerdisposed on the substrate, and a drift layer disposed on the bufferlayer. In this context, uniformity of carrier density may be less than10% and a defect density is less than 0.5 count/cm²; and the C/Si ratioof the buffer layer 3B may be controlled to be lower than the C/Si ratioof the drift layer 3D.

The off angle may be 2 degrees.

Moreover, a growth temperature of the SiC epitaxial growth layer may bewithin a range of 1630° C. to 1690° C.

Moreover, a growth pressure of the SiC epitaxial growth layer may bewithin a range of 3 kPa to 11 kPa.

Moreover, a flow rate of carrier gas at the time of formation of the SiCepitaxial growth layer may be within a range of 100 slm to 150 slm.

The Si compound may contain any one material of SiH₄, SiH₃F, SiH₂F₂,SiHF₃, or SiF₄, for example. Other compounds containing chlorine (Cl)may be used as the Si compound.

Moreover, the C compound may contain any one material of C₃H₈, C₂H₄,C₂H₂, CF₄, C₂F₆, C₃F₈, C₄F₆, C₄F₈, C₅F₈, CHF₃, CH₂F₂, CH₃F, or C₂HF₅.Other compounds containing chlorine (Cl) may be used as the C compound.

Moreover, the SiC epitaxial growth layer may contain any one material of4H—SiC, 6H—SiC, 2H—SiC, or 3C—SiC.

A diameter of the substrate 2 having an off angle of less than 4 may beequal to or greater than 100 mm, for example.

The substrate 2 having an off angle of less than 4 may contain 4H—SiC or6H—SiC. Any one BN, AlN, Al₂O₃, Ga₂O₃, diamond, carbon, or graphite maybe contained instead of the SiC.

In the SiC epitaxial growth for the SiC epitaxial wafer according to theembodiments, at least one of H₂, Ar, HCl, and the F₂ is applicable ascarrier gas.

As the materials for dopant, N (nitrogen) or TMA can be applied.

(Fourth CVD Apparatus)

As shown in FIG. 33, a schematic configuration example of a fourth CVDapparatus applicable to the SiC epitaxial growth, in a manufacturingapparatus 200 of the SiC epitaxial wafer according to the embodimentsincludes: a gas injection port 140; a gas exhaust port 160; a heatingunit 100; and a horizontal-type reactor 130.

As a heating method of the heating unit 100, resistance heating,induction heating using a coil, lamp heating, etc. are adoptable. In thecase of the induction heating method, a structural member made fromcarbon (not shown in FIG. 14) disposed near the wafer, the structuralmember made from carbon produces heat, and then the wafer in contactwith the structural member is heated or the wafer is heated withradiation from the structural member made from carbon.

In the horizontal-type reactor 130, a plurality pieces of the SiCepitaxial wafers 1 can be disposed in a face up manner or face downmanner.

While the material gas is supplied from the gas injection port 140 ofthe horizontal-type reactor 130, passes through the plurality pieces ofthe SiC epitaxial wafers 1, and then is exhausted from the gas exhaustport 160, the materials which flows on the surface of the pluralitypieces of the SiC epitaxial wafers 1 react, thereby forming the SiCepitaxial growth layer.

In this case, a material gas supplied when forming the SiC epitaxialgrowth layer on the substrate having the off angle of less than 4degrees contains an Si compound used as a supply source of Si, andCarbon (C) compound used as a supply source of Carbon (C). Theuniformity of carrier density may be less than 10%, and the defectdensity may be less than 1 count/cm²; and a C/Si ratio between the Sicompound and the Carbon (C) compound is within a range of 0.7 to 0.95.

Moreover, the SiC epitaxial growth layer may include a buffer layerdisposed on the substrate, and a drift layer disposed on the bufferlayer. In this context, uniformity of carrier density may be less than10% and a defect density is less than 0.5 count/cm²; and the C/Si ratioof the buffer layer 3B may be controlled to be lower than the C/Si ratioof the drift layer 3D.

The off angle may be 2 degrees.

Moreover, a growth temperature of the SiC epitaxial growth layer may bewithin a range of 1630° C. to 1690° C.

Moreover, a growth pressure of the SiC epitaxial growth layer may bewithin a range of 3 kPa to 11 kPa.

Moreover, a flow rate of carrier gas at the time of formation of the SiCepitaxial growth layer may be within a range of 100 slm to 150 slm.

The Si compound may contain any one material of SiH₄, SiH₃F, SiH₂F₂,SiHF₃, or SiF₄, for example. Other compounds containing chlorine (Cl)may be used as the Si compound.

Moreover, the C compound may contain any one material of C₃H₈, C₂H₄,C₂H₂, CF₄, C₂F₆, C₃F₈, C₄F₆, C₄F₈, C₅F₈, CHF₃, CH₂F₂, CH₃F, or C₂HF₅.Other compounds containing chlorine (Cl) may be used as the C compound.

Moreover, the SiC epitaxial growth layer may contain any one material of4H—SiC, 6H—SiC, 2H—SiC, or 3C—SiC.

A diameter of the substrate 2 having an off angle of less than 4 may beequal to or greater than 100 mm, for example.

The substrate 2 having an off angle of less than 4 may contain 4H—SiC or6H—SiC. Any one BN, AlN, Al₂O₃, Ga₂O₃, diamond, carbon, or graphite maybe contained instead of the SiC.

In the SiC epitaxial growth for the SiC epitaxial wafer according to theembodiments, at least one of H₂, Ar, HCl, and the F₂ is applicable ascarrier gas.

As the materials for dopant, N (nitrogen) or TMA can be applied.

The above-mentioned SiC epitaxial wafer 1 according to the embodimentsis applicable to fabricating of various kinds of SiC semiconductorelements, for example. Hereinafter, there will be shown examples of aSiC Schottky Barrier Diode (SiC-SBD), a SiC Trench-gate type Metal OxideSemiconductor Field Effect Transistor (Sic-TMOSFET), and a SiCplanar-gate type MOSFET, as those examples.

(SiC-SBD)

FIG. 34 shows a schematic cross-sectional structure of SiC-SBD 21fabricated using the SiC epitaxial wafer according to the embodiments.

As shown in FIG. 34, the SiC-SBD 21 fabricated using the SiC epitaxialwafer according to the embodiments includes a SiC epitaxial wafer 1. TheSiC epitaxial wafer 1 includes: an n⁺ type SiC substrate 2 having theoff angle of less than 2 degrees (of which an impurity concentration isapproximately 1×10¹⁸ cm⁻³ to approximately 1×10²¹ cm⁻³, for example);and an n⁻ type SiC epitaxial growth layer 3 (of which an impurityconcentration is approximately 5×10¹⁴ cm⁻³ to approximately 5×10¹⁶ cm⁻³,for example).

In this case, a material gas supplied when forming the SiC epitaxialgrowth layer 3 on the SiC substrate having the off angle of less than 4degrees contains an Si compound used as a supply source of Si, andCarbon (C) compound used as a supply source of Carbon (C). Theuniformity of carrier density may be less than 10%, and the defectdensity may be less than 1 count/cm²; and a C/Si ratio between the Sicompound and the Carbon (C) compound is within a range of 0.7 to 0.95.

Moreover, the SiC epitaxial growth layer 3 may include a buffer layerdisposed on the SiC substrate having the off angle of less than 4degrees, and a drift layer disposed on the buffer layer. In thiscontext, uniformity of carrier density may be less than 10% and a defectdensity is less than 0.5 count/cm²; and the C/Si ratio of the bufferlayer 3B may be controlled to be lower than the C/Si ratio of the driftlayer 3D.

The off angle may be 2 degrees.

Moreover, a growth temperature of the SiC epitaxial growth layer 3 maybe within a range of 1630° C. to 1690° C.

Moreover, a growth pressure of the SiC epitaxial growth layer 3 may bewithin a range of 3 kPa to 11 kPa.

Moreover, a flow rate of carrier gas at the time of formation of the SiCepitaxial growth layer 3 may be within a range of 100 slm to 150 slm.

The Si compound may contain any one material of SiH₄, SiH₃F, SiH₂F₂,SiHF₃, or SiF₄, for example. Other compounds containing chlorine (Cl)may be used as the Si compound.

Moreover, the C compound may contain any one material of C₃H₈, C₂H₄,C₂H₂, CF₄, C₂F₆, C₃F₈, C₄F₆, C₄F₈, C₅F₈, CHF₃, CH₂F₂, CH₃F, or C₂HF₅.Other compounds containing chlorine (Cl) may be used as the C compound.

Moreover, the SiC epitaxial growth layer may contain any one material of4H—SiC, 6H—SiC, 2H—SiC, or 3C—SiC.

A diameter of the substrate 2 having an off angle of less than 4 may beequal to or greater than 100 mm, for example.

The substrate 2 having an off angle of less than 4 may contain 4H—SiC or6H—SiC. Any one BN, AlN, Al₂O₃, Ga₂O₃, diamond, carbon, or graphite maybe contained instead of the SiC.

In the SiC epitaxial growth for the SiC epitaxial wafer according to theembodiments, at least one of H₂, Ar, HCl, and the F₂ is applicable ascarrier gas.

As an n type doping impurities, nitrogen (N), phosphorus (P), arsenic(As), etc. are applicable, for example.

As p type doping impurities, TMA etc. are applicable, for example.

A back side surface ((000-1) C surface) of the SiC substrate 2 includesa cathode electrode 22 so as to cover the whole region of the back sidesurface, and the cathode electrode 22 is connected to a cathode terminalK.

A surface 10 ((0001) Si surface) of the SiC epitaxial growth layer 3includes a contact hole 24 to which a part of the SiC epitaxial growthlayer 3 is exposed as an active region 23, and a field insulating film26 is formed at a field region 25 which surrounding the active region23.

Although the field insulating film 26 includes silicon oxide (SiO₂), thefield insulating film 26 may include other insulating materials, e.g.silicon nitride (SiN). An anode electrode 27 is formed on the fieldinsulating film 26, and the anode electrode 27 is connected to an anodeterminal A.

Near the surface 10 (surface portion) of the SiC epitaxial growth layer3, a p type Junction Termination Extension (JTE) structure 28 is formedso as to be contacted with the anode electrode 27. The JTE structure 28is formed along an outline of the contact hole 24 so as to extend fromthe outside to inside of the contact hole 24 of the field insulatingfilm 26.

According to the SiC-SBD 21 fabricated using the SiC epitaxial waferaccording to the embodiments, a leakage current can be reduced.

(SiC-TMOSFET)

FIG. 35 shows a schematic cross-sectional structure of the SiC-TMOSFET31 fabricated using the SiC epitaxial wafer according to theembodiments.

As shown in FIG. 35, the SiC-TMOSFET 31 fabricated using the SiCepitaxial wafer according to the embodiments includes a SiC epitaxialwafer 1. The SiC epitaxial wafer 1 includes: an n⁺ type SiC substrate 2having the off angle of less than 2 degrees (of which an impurityconcentration is approximately 1×10¹⁸ cm⁻³ to approximately 1×10²¹ cm⁻³,for example); and an n⁻ type SiC epitaxial growth layer 3 (of which animpurity concentration is approximately 5×10¹⁴ cm⁻³ to approximately5×10¹⁶ cm⁻³, for example).

In this case, a material gas supplied when forming the SiC epitaxialgrowth layer 3 on the SiC substrate having the off angle of less than 4degrees contains an Si compound used as a supply source of Si, andCarbon (C) compound used as a supply source of Carbon (C). Theuniformity of carrier density may be less than 10%, and the defectdensity may be less than 1 count/cm²; and a C/Si ratio between the Sicompound and the Carbon (C) compound is within a range of 0.7 to 0.95.

Moreover, the SiC epitaxial growth layer 3 may include a buffer layerdisposed on the SiC substrate having the off angle of less than 4degrees, and a drift layer disposed on the buffer layer. In thiscontext, uniformity of carrier density may be less than 10% and a defectdensity is less than 0.5 count/cm²; and the C/Si ratio of the bufferlayer 3B may be controlled to be lower than the C/Si ratio of the driftlayer 3D.

The off angle may be 2 degrees.

Moreover, a growth temperature of the SiC epitaxial growth layer 3 maybe within a range of 1630° C. to 1690° C.

Moreover, a growth pressure of the SiC epitaxial growth layer 3 may bewithin a range of 3 kPa to 11 kPa.

Moreover, a flow rate of carrier gas at the time of formation of the SiCepitaxial growth layer 3 may be within a range of 100 slm to 150 slm.

The Si compound may contain any one material of SiH₄, SiH₃F, SiH₂F₂,SiHF₃, or SiF₄, for example. Other compounds containing chlorine (Cl)may be used as the Si compound.

Moreover, the C compound may contain any one material of C₃H₈, C₂H₄,C₂H₂, CF₄, C₂F₆, C₃F₈, C₄F₆, C₄F₈, C₅F₈, CHF₃, CH₂F₂, CH₃F, or C₂HF₅.Other compounds containing chlorine (Cl) may be used as the C compound.

Moreover, the SiC epitaxial growth layer may contain any one material of4H—SiC, 6H—SiC, 2H—SiC, or 3C—SiC.

A diameter of the substrate 2 having an off angle of less than 4 may beequal to or greater than 100 mm, for example.

The substrate 2 having an off angle of less than 4 may contain 4H—SiC or6H—SiC. Any one BN, AlN, Al₂O₃, Ga₂O₃, diamond, carbon, or graphite maybe contained instead of the SiC.

In the SiC epitaxial growth for the SiC epitaxial wafer according to theembodiments, at least one of H₂, Ar, HCl, and the F₂ is applicable ascarrier gas.

As an n type doping impurities, nitrogen (N), phosphorus (P), arsenic(As), etc. are applicable, for example.

As p type doping impurities, TMA etc. are applicable, for example.

A back side surface ((000-1) C surface) of the SiC substrate 2 includesa drain electrode 32 so as to cover the whole region of the back sidesurface, and the drain electrode 32 is connected to a drain terminal D.

Near the surface 10 ((0001) Si surface) (surface portion) of the SiCepitaxial growth layer 3, a p type body region 33 (of which an impurityconcentration is approximately 1×10²⁶ cm⁻³ to approximately 1×10¹⁹ cm⁻³,for example) is formed. In the SiC epitaxial growth layer 3, a portionat a side of the SiC substrate 2 with respect to the body region 33 isan n⁻ type drain region 34 where a state after the epitaxial growth isstill kept.

A gate trench 35 is formed in the SiC epitaxial growth layer 3. The gatetrench 35 passes through the body region 33 from the surface 10 of theSiC epitaxial growth layer 3, and a deepest portion of the gate trench35 extends to the drain region 34.

A gate insulating film 36 is formed on an inner surface of the gatetrench 35 and the surface 10 of the SiC epitaxial growth layer 3 so asto cover the whole of the inner surface of the gate trench 35. Moreover,a gate electrode 37 is embedded in the gate trench 35 by filling up theinside of the gate insulating film 36 with polysilicon, for example. Agate terminal G is connected to the gate electrode 37.

An n⁺ type source region 38 forming a part of a side surface of the gatetrench 35 is formed on a surface portion of the body region 33.

Moreover, a p⁺ type body contact region 39 (of which an impurityconcentration is approximately 1×10¹⁸ cm⁻³ to approximately 1×10²¹ cm⁻³,for example) which passes through the source region 38 from the surface10 and is connected to the body region 33 is formed on the SiC epitaxialgrowth layer 3.

An interlayer insulating film 40 including SiO₂ is formed on the SiCepitaxial growth layer 3. A source electrode 42 is connected to thesource region 38 and the body contact region 39 through a contact hole41 formed in the interlayer insulating film 40. A source terminal S isconnected to the source electrode 42.

A predetermined voltage (voltage equal to or greater than a gatethreshold voltage) is applied to the gate electrode 37 in a state wherea predetermined potential difference is generated between the sourceelectrode 42 and the drain electrode 32 (between the source and thedrain). Thereby, a channel can be formed by an electric field from thegate electrode 37 near the interface between the gate insulating film 36and the body region 33. Thus, an electric current can be flowed betweenthe source electrode 42 and the drain electrode 32, and therebySiC-TMOSFET 31 can be turned ON state.

The SiC-TMOSFET 31 fabricated using the SiC epitaxial wafer according tothe embodiments can improve a carrier mobility and can offer enhancedspeed.

(SiC Planar-Gate Type MOSFET)

FIG. 36 shows a schematic cross-sectional structure of the planar-gatetype SiC-MOSFET fabricated using the SiC epitaxial wafer according tothe embodiments.

As shown in FIG. 36, the planar-gate-type SiC-TMOSFET 51 fabricatedusing the SiC epitaxial wafer according to the embodiments includes aSiC epitaxial wafer 1. The SiC epitaxial wafer 1 includes: an n⁺ typeSiC substrate 2 having the off angle of less than 2 degrees (of which animpurity concentration is approximately 1×10¹⁸ cm⁻³ to approximately1×10²¹ cm⁻³, for example); and an n⁻ type SiC epitaxial growth layer 3(of which an impurity concentration is approximately 5×10¹⁴ cm⁻³ toapproximately 5×10¹⁶ cm⁻³, for example).

In this case, a material gas supplied when forming the SiC epitaxialgrowth layer 3 on the SiC substrate having the off angle of less than 4degrees contains an Si compound used as a supply source of Si, andCarbon (C) compound used as a supply source of Carbon (C). Theuniformity of carrier density may be less than 10%, and the defectdensity may be less than 1 count/cm²; and a C/Si ratio between the Sicompound and the Carbon (C) compound is within a range of 0.7 to 0.95.

Moreover, the SiC epitaxial growth layer 3 may include a buffer layerdisposed on the SiC substrate having the off angle of less than 4degrees, and a drift layer disposed on the buffer layer. In thiscontext, uniformity of carrier density may be less than 10% and a defectdensity is less than 0.5 count/cm²; and the C/Si ratio of the bufferlayer 3B may be controlled to be lower than the C/Si ratio of the driftlayer 3D.

The off angle may be 2 degrees.

Moreover, a growth temperature of the SiC epitaxial growth layer 3 maybe within a range of 1630° C. to 1690° C.

Moreover, a growth pressure of the SiC epitaxial growth layer 3 may bewithin a range of 3 kPa to 11 kPa.

Moreover, a flow rate of carrier gas at the time of formation of the SiCepitaxial growth layer 3 may be within a range of 100 slm to 150 slm.

The Si compound may contain any one material of SiH₄, SiH₃F, SiH₂F₂,SiHF₃, or SiF₄, for example. Other compounds containing chlorine (Cl)may be used as the Si compound.

Moreover, the C compound may contain any one material of C₃H, C₂H₄,C₂H₂, CF₄, C₂F₆, C₃F₈, C₄F₆, C₄F₈, C₅F₈, CHF₃, CH₂F₂, CH₃F, or C₂HF₅.Other compounds containing chlorine (Cl) may be used as the C compound.

Moreover, the SiC epitaxial growth layer may contain any one material of4H—SiC, 6H—SiC, 2H—SiC, or 3C—SiC.

A diameter of the substrate 2 having an off angle of less than 4 may beequal to or greater than 100 mm, for example.

The substrate 2 having an off angle of less than 4 may contain 4H—SiC or6H—SiC. Any one BN, AlN, Al₂O₃, Ga₂O₃, diamond, carbon, or graphite maybe contained instead of the SiC.

In the SiC epitaxial growth for the SiC epitaxial wafer according to theembodiments, at least one of H₂, Ar, HCl, and the F₂ is applicable ascarrier gas.

As an n type doping impurities, nitrogen (N), phosphorus (P), arsenic(As), etc. are applicable, for example.

As p type doping impurities, TMA etc. are applicable, for example.

A back side surface ((000-1) C surface) of the SiC substrate 2 includesa drain electrode 52 so as to cover the whole region of the back sidesurface, and the drain electrode 52 is connected to a drain terminal D.

Near the surface 10 ((0001) Si surface) (surface portion) of the SiCepitaxial growth layer 3, a p type body region 53 (of which an impurityconcentration is approximately 1×10¹⁶ cm⁻³ to approximately 1×10¹⁹ cm⁻³,for example) is formed in a well shape. In the SiC epitaxial growthlayer 3, a portion at a side of the SiC substrate 2 with respect to thebody region 53 is an n-type drain region 54 where a state after theepitaxial growth is still kept.

An n⁺ type source region 55 is formed on a surface portion of the bodyregion 53 with a certain space from a periphery of the body region 53.

A p⁺ type body contact region 56 (of which an impurity concentration isapproximately 1×10¹⁸ cm⁻³ to approximately 1×10²¹ cm⁻³, for example) isformed inside of the source region 55. The body contact region 56 passesthrough the source region 55 in a depth direction, and is connected tothe body region 53.

A gate insulating film 57 is formed on the surface 10 of the SiCepitaxial growth layer 3. The gate insulating film 57 covers the portionsurrounding the source region 55 in the body region 53 (peripheralportion of the body region 53), and an outer peripheral portion of thesource region 55.

A gate electrode 58 including polysilicon, for example, is formed on thegate insulating film 57. The gate electrode 58 is opposed to theperipheral portion of the body region 53 by sandwiching the gateinsulating film 57. A gate terminal G is connected to the gate electrode58.

An interlayer insulating film 59 including SiO₂ is formed on the SiCepitaxial growth layer 3. A source electrode 61 is connected to thesource region 55 and the body contact region 56 through a contact hole60 formed in the interlayer insulating film 59. A source terminal S isconnected to the source electrode 61.

A predetermined voltage (voltage equal to or greater than a gatethreshold voltage) is applied to the gate electrode 58 in a state wherea predetermined potential difference is generated between the sourceelectrode 61 and the drain electrode 52 (between the source and thedrain). Thereby, a channel can be formed by an electric field from thegate electrode 58 near the interface between the gate insulating film 57and the body region 53. Thus, an electric current can be flowed betweenthe source electrode 61 and the drain electrode 52, and thereby theplanar-gate type MOSFET 51 can be turned ON state.

The planar-gate type MOSFET 51 also can improve a carrier mobility andcan offer enhanced speed, similarly to the SiC-TMOSFET 31 shown in FIG.35.

Although the embodiments have been explained above, the embodiments canalso be implemented with other configurations.

For example, the principal surface 4 (substrate surface) of the SiCsubstrate 2 may be inclined in the OFF direction of [−1100] axis withrespect to the (0001) surface by the off angle θ less than 4 degrees.Although illustration is omitted, MOS capacitors can also be fabricatedusing the SiC epitaxial wafer 1 according to the embodiments. Accordingto the MOS capacitors, a yield and reliability can be improved.Moreover, with regard to the reliability, initial failures can bereduced.

Although illustration is omitted, bipolar junction transistors can alsobe fabricated using the SiC epitaxial wafer according to theembodiments. In addition, the SiC epitaxial wafer according to theembodiments can also be used for fabricating of SiC-pn diodes, SiCInsulated Gate Bipolar Transistor (IGBT), SiC complementary MOSFET, etc.

According to the SiC epitaxial wafer according to the embodiments,defect regions on the surface or interface of the SiC epitaxial growthlayer can be reduced. Therefore, a leakage current, nonuniformity of theoxide film thickness, interface state density, surface recombination,etc. are reduced, and thereby field effect mobility can be improved.Accordingly, there can be provided the high quality SiC semiconductordevice having high reliability.

As explained above, the embodiments provide: the high-quality SiCepitaxial wafer excellent in film thickness uniformity and uniformity ofcarrier density, having the small number of surface defects, and capableof reducing costs, also in low-off angle SiC substrates on SiC epitaxialgrowth; the manufacturing apparatus of such a SiC epitaxial wafer; thefabrication method of such a SiC epitaxial wafer; and the semiconductordevice.

Other Embodiments

As mentioned above, although the SiC epitaxial wafer, the manufacturingapparatus of the SiC epitaxial wafer, the fabrication method of the SiCepitaxial wafer, and the semiconductor device have been described, as adisclosure including associated description and drawings to be construedas illustrative, not restrictive. This disclosure makes clear a varietyof alternative embodiments, working examples, and operational techniquesfor those skilled in the art.

Such being the case, the embodiments cover a variety of embodiments,whether described or not.

INDUSTRIAL APPLICABILITY

The semiconductor device to which the SiC epitaxial wafer according tothe embodiments is applied can be applied to wide applicable fields,e.g., power modules for inverter circuits for driving electric motorsutilized as sources of power of electric vehicles (including hybridcars), trains, industrial robots; and power modules for invertercircuits for transforming electric power generated by electricgenerators (e.g., solar cells, wind power generators, and the like (inparticular private electric generators)) into electric power forcommercial power sources, etc.

What is claimed is:
 1. A SiC epitaxial wafer comprising: a substratehaving off angle; a first SiC epitaxial growth layer disposed on thesubstrate; and a second SiC epitaxial growth layer disposed on the firstSiC epitaxial growth layer, wherein the first SiC epitaxial growth layeris thinner than the SiC second epitaxial growth layer and has a lowerdefect density than a defect density of the second epitaxial growthlayer, wherein the uniformity of carrier density of the second SiCepitaxial growth layer is less than 10%, and the defect density of thesecond SiC epitaxial growth layer is less than 1 count/cm².
 2. The SiCepitaxial wafer according to claim 1, wherein the first SiC epitaxialgrowth layer comprises a buffer layer disposed on the substrate, and thesecond SiC epitaxial growth layer comprises a drift layer disposed onthe buffer layer, wherein a Si (silicon) compound is used for a supplysource of Si, and a C (carbon) compound is used as a supply source of C,for the first and second SiC epitaxial growth layers; the uniformity ofcarrier density is less than 10%, and the defect density is less than0.5 count/cm²; and the C/Si ratio of the Si compound and the C compoundin the buffer layer is controlled to be lower than the C/Si ratio of theSi compound and the C compound in the drift layer.
 3. The SiC epitaxialwafer according to claim 1, wherein the off angle is equal to or lessthan 4 degrees.
 4. The SiC epitaxial wafer according to claim 1, whereinthe Si compound comprises at least one material selected from the groupconsisting of SiH₄, SiH₃F, SiH₂F₂, SiHF₃, and SiF₄.
 5. The SiC epitaxialwafer according to claim 1, wherein the C compound comprises at leastone material selected from the group consisting of C₃H₈, C₂H₄, C₂H₂,CF₄, C₂F₆, C₃F₈, C₄F₆, C₄F₈, C₅F₈, CHF₃, CH₂F₂, CH₃F, and C₂HF₅.
 6. TheSiC epitaxial wafer according to claim 1, wherein the first and secondSiC epitaxial growth layers comprise one material selected from thegroup consisting of 4H—SiC, 6H—SiC, 2H—SiC, and 3C—SiC.
 7. The SiCepitaxial wafer according to claim 1, wherein a diameter of thesubstrate is equal to or greater than 100 mm.
 8. The SiC epitaxial waferaccording to claim 1, wherein the substrate comprises one materialselected from the group consisting of 4H—SiC, 6H—SiC, BN, AlN, Al₂O₃,Ga₂O₃, diamond, carbon, and graphite.
 9. A semiconductor devicecomprising a SiC epitaxial wafer, wherein the SiC epitaxial wafercomprises: a substrate having low-off angle of less than 4 degrees; anda SiC epitaxial growth layer disposed on the substrate, wherein a Si(silicon) compound is used for a supply source of Si, and a C (carbon)compound is used as a supply source of C, for the SiC epitaxial growthlayer, wherein the uniformity of carrier density is less than 10%, andthe defect density is less than 1 count/cm²; and a C/Si ratio betweenthe Si compound and the C compound is within a range of 0.7 to 0.95. 10.The semiconductor device according to claim 9, wherein the semiconductordevice comprises one selected from the group consisting of a SiCSchottky barrier diode, a SiC-MOSFET, a SiC bipolar junction transistor,a SiC diode, a SiC thyristor, and a SiC insulated gate bipolartransistor.